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    INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY


    ENVIRONMENTAL HEALTH CRITERIA 16





    RADIOFREQUENCY AND MICROWAVES




    This report contains the collective views of an international group of
    experts and does not necessarily represent the decisions or the stated
    policy of either the World Health Organization, United Nations
    Environment Programme, or the International Radiation Protection Association.

    Published under the joint sponsorship of
    the United Nations Environment Programme,
    World Health Organization and the International
    Radiation Protection Association

    World Health Organization
    Geneva, 1981

    ISBN 92 4 154076 1

    (c) World Health Organization 1981

        Publications of the World Health Organization enjoy copyright
    protection in accordance with the provisions of Protocol 2 of the
    Universal Copyright Convention. For rights of reproduction or
    translation of WHO publications, in part or  in toto, application
    should be made to the Office of Publications, World Health
    Organization, Geneva, Switzerland. The World Health Organization
    welcomes such applications.

        The designations employed and the presentation of the material in
    this publication do not imply the expression of any opinion whatsoever
    on the part of the Secretariat of the World Health Organization
    concerning the legal status of any country, territory, city or area or
    of its authorities, or concerning the delimitation of its frontiers or
    boundaries.

        The mention of specific companies or of certain manufacturers'
    products does not imply that they are endorsed or recommended by the
    World Health Organization in preference to others of a similar nature
    that are not mentioned. Errors and omissions excepted, the names of
    proprietary products are distinguished by initial capital letters.


    CONTENTS

    ENVIRONMENTAL HEALTH CRITERIA FOR RADIOFREQUENCY AND MICROWAVES

    1. SUMMARY AND RECOMMENDATIONS FOR FURTHER STUDIES

         1.1. Summary
              1.1.1. Physical characteristics in relation to biological
                      effects
              1.1.2. Sources and control of exposure
              1.1.3. Biological effects in experimental animals
              1.1.4. Power density ranges in relation to health effects
              1.1.5. Exposure effects in man
              1.1.6. Health risk evaluation as a basis for exposure
                      limits

         1.2. Recommendations for further studies, exposure limits, and
              protective measures
              1.2.1. General recommendations
              1.2.2. Measurement techniques
              1.2.3. Safety procedures
              1.2.4. Biological investigations
              1.2.5. Epidemiological investigations
              1.2.6. Exposure limits and emission standards
                      1.2.6.1   Occupational exposure limits
                      1.2.6.2   Exposure limits for the general population
                      1.2.6.3   Emission standards
                      1.2.6.4   Implementation of standards
                      1.2.6.5   Other protective measures
                      1.2.6.6   Studies related to the establishment of
                                limits

    2. MAGNITUDE OF EXPOSURE TO MICROWAVE AND RF RADIATION AND SOURCES
         OF CONCERN

    3. PROPERTIES OF MICROWAVE AND RADIOFREQUENCY (RF) RADIATION

         3.1. Units of radiation
         3.2. Other physical considerations

    4. SOURCES AND CONDITIONS OF EXPOSURE

         4.1. Natural background sources
         4.2. Man-made sources
              4.2.1. Deliberate emitters
              4.2.2. Sources of unintentional radiation

         4.3. Estimating exposure levels
              4.3.1. Far-field exposure
              4.3.2. Near-field exposure

         4.4. Facilities for controlled exposure
              4.4.1. Free space standard field method
              4.4.2. Guided wave methods
              4.4.3. Standard probe method

    5. MEASURING INSTRUMENTS

         5.1. General principles
         5.2. Types of instruments in common use
              5.2.1. Diode rectifier
              5.2.2. Bolometer
              5.2.3. Thermocouple

    6. MICROWAVE AND RF ENERGY ABSORPTION IN BIOLOGICAL SYSTEMS

         6.1. Methods of computation
         6.2. Experimental methods
         6.3. Energy absorption
         6.4. Molecular absorption

    7. BIOLOGICAL EFFECTS IN EXPERIMENTAL ANIMALS

         7.1. Hyperthermia and gross thermal effects
         7.2. Effects on the eye
         7.3. Neuroendocrine effects
         7.4. Nervous system and behavioural effects
         7.5. Effects on the blood forming and immunocompetent cell
              systems
         7.6. Genetic and other effects in cell systems
         7.7. Effects on reproduction and development

    8. HEALTH EFFECTS IN MAN

         8.1. Effects of occupational exposure
              8.1.1. Effects on the eyes
              8.1.2. Effects on reproduction and genetic effects
              8.1.3. Cardiovascular effects

         8.2. Medical exposure

    9. RATIONALES FOR MICROWAVE AND RF RADIATION PROTECTION STANDARDS

         9.1. Principles
         9.2. Group 1 standards
         9.3. Group 2 standards
         9.4. Group 3 standards
         9.5. RF radiation standards (100 kHz to 300 MHz)

    10. SAFETY PROCEDURES FOR OCCUPATIONALLY EXPOSED PERSONNEL

         10.1. Procedures for reducing occupational exposure

    11. ASSESSMENT OF DATA ON BIOLOGICAL EFFECTS AND RECOMMENDED EXPOSURE
         LIMITS

    REFERENCES

    GLOSSARY

    ANNEX
    

    NOTE TO READERS OF THE CRITERIA DOCUMENTS

        While every effort has been made to present information in the
    criteria documents as accurately as possible without unduly delaying
    their publication, mistakes might have occurred and are likely to
    occur in the future. In the interest of all users of the environmental
    health criteria documents, readers are kindly requested to communicate
    any errors found to the Division of Environmental Health, World Health
    Organization, Geneva, Switzerland, in order that they may be included
    in corrigenda which will appear in subsequent volumes.

        In addition, experts in any particular field dealt with in the
    criteria documents are kindly requested to make available to the WHO
    Secretariat any important published information that may have
    inadvertently been omitted and which may change the evaluation of
    health risks from exposure to the environmental agent under
    examination, so that the information may be considered in the event of
    updating and re-evaluation of the conclusions contained in the
    criteria documents.

    WHO/IRPA TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR
    RADIOFREQUENCY AND MICROWAVES

     Members

    Dr V. Akimenko, A. N. Marzeev Institute of General and Communal
        Hygiene, Kiev, USSR

    Professor P. Czerski, National Research Institute of Mother and Child,
        Warsaw, Poland  (Rapporteur)a

    Mme A. Duchne, Dpartement de Protection, Centre d'Etudes nuclaires,
        Fontenay-aux-Roses, Francea

    Dr M. Faber, Finsen Institute, Finsen Laboratory, Copenhagen,
        Denmarka

    Professor M. Grandolfo, Radiation Laboratory, Higher Institute of
        Health, Rome, Italy

    Mr F. Harlen, National Radiological Protection Board, Harwell, England

    Dr H. Jammet, Dpartement de Protection, Centre d'Etudes nuclaires,
        Fontenay-aux-Roses, Francea

    Dr J. Kupfer, Central Institute for Occupational Medicine of the GDR,
        Berlin, German Democratic Republic  (Vice-Chairman) 

    Dr M. Repacholi, Health Protection Branch, Department of National
        Health and Welfare, Ottawa, Canada

    Dr B. Servantie, E.A.S.S.M. -- Centre d'Etudes et de Recherche de
        Biophysiologie, Toulon Naval, France

    Dr M. Shore, Bureau of Radiological Health, Food and Drug
        Administration, Department of Health, Education and Welfare,
        Rockville, MD, USA  (Chairman)

              

    a  From the Committee on Non-Ionizing Radiation of the International
       Radiation Protection Association


     Representatives of other Organizations

    Mr H. Pouliquen, International Telecommunications Union, Geneva,
        Switzerland

    Dr G. Verfaillie, Commission of European Communities, Brussels,
        Belgium

     Secretariat

    Mr S. Fluss, Health and Biomedical Information Programme, WHO, Geneva,
        Switzerland

    Dr E. Komarov, Environmental Health Criteria and Standards, Division
        of Environmental Health, WHO, Geneva, Switzerland  (Secretary)



        THE INTERNATIONAL SYSTEM OF UNITS (SI) COMMONLY USED IN ELECTROMAGNETICS
                                                                                                   

         Name of Dimension        Symbol for
         of Quantity              quantity                    SI unit and symbol
                                                                                                   

    Admittance                    Y                           siemens (S)
    Area. surface                 S                           square metre (m2)
    Attenuation                   A                           1 (Non-SI unit is the dB)

    Attenuation coefficient       alpha                       reciprocal metre (1/m)

    Capacitance                   C                           farad (F)
    Charge                        Q                           coulomb (C)
    Charge, volume density of     q                           coulomb per cubic metre (C/m3)
    Conductance, electric         G                           siemens (S)
    Conductivity                                             siemens per metre (S/m)
    Current                       I                           ampere (A)
    Current density               J                           ampere per square metre (A/m2)
    Dielectric polarization       P                           coulomb per square metre (C/m2)
                                  (P = D - epsilono E)
    Dipole moment (electric)      p                           coulomb  metre (C  m)
    Dipole moment (magnetic)      j                           weber metre (Wb  m)
    Electric field strength       K                           volt per metre (V/m)
    Electric flux                 phi                         coulomb (C)
    Electric flux density         D                           coulomb per square metre (C/m3)
    Electric polarization         D1                          coulomb per square metre (C/m2)
    Electric potential            V                           volt (V)
    Electric susceptibility       chie                        (see glossary)
                                  (chie = epsilonr - 1)
    Energy or work                E                           joule (J)
    Energy density                w                           joule per cubic metre (J/m3)
    Frequency                     f                           hertz (Hz)
    Impedance                     Z                           ohm (OMEGA)
    Impedance, characteristic     Zo                          ohm (OMEGA)
    Inductance, mutual            M                           henry (H)
                                                                                                   

    (Cont'd)
                                                                                                   

         Name of Dimension        Symbol for
         of Quantity              quantity                    SI unit and symbol
                                                                                                   

    Length                        I                           metre (m)
    Magnetic field strength       H                           ampere per metre (A/m)
    Magnetic flux                 PHI                         weber (Wb)
    Magnetic flux density         B                           tesla (T)
    Magnetic polarization         B1                          tesla (T)
    Permeability                                             henry per metre (H/m)
    Relative permeability         r                          (see glossary)
                                  (r= /o)
    Permittivity                  epsilon                     farad per metre (F/m)
    Phase coefficient                                        radian per metre (rad/m)
    Power                         P                           watt (w)
    Power gain                    G                           1 (Non-SI unit is the dB)
                                  (G = 10 log (P2/P1))
    Poynting vector               S                           watt per square metre (W/m2)
    Propagation coefficient       gamma                       Units for alpha and  given separately
                                  (gamma = alpha + j)
                                  where alpha = attenuation
                                  coefficient and  =
                                  phase coefficient
    Radiant intensity             I                           watt per steradian (W/sr)
    Reactance                     X                           ohm (OMEGA)
    Wavelength                    lambda                      metre (m)
                                                                                                   

    a  The SI units for non-ionizing radiation have not been completely developed.
       Terms used in the text but not defined in this table can be found in the
       glossary at the end of the document.
    

    ENVIRONMENTAL HEALTH CRITERIA FOR RADIOFREQUENCY AND MICROWAVES

        A Joint WHO/IRPA Task Group on Environmental Health Criteria for
    Radiofrequency and Microwaves met in Geneva from 18-22 December 1978.
    Dr B. H. Dieterich, Director, Division of Environmental Health, opened
    the meeting on behalf of the Director-General. The Task Group reviewed
    and revised the draft criteria document, made an evaluation of the
    health risks of exposure to radiofrequency and microwaves, and
    considered rationales for the development of exposure limits.

        In November 1971, the WHO Regional Office for Europe convened a
    Working Group meeting in The Hague which recommended,  inter alia,
    that the protection of man from microwave radiation hazards should be
    considered a priority activity in the field of non-ionizing radiation
    protection. To implement these recommendations, the Regional Office
    decided to prepare the manual on "Non-Ionizing Radiation Protection",
    which will include a chapter on microwave radiation (WHO, 1981).

        In 1973, a symposium, sponsored by WHO and the Governments of
    Poland and the USA, was held in Warsaw, on the biological effects and
    health hazards of microwave radiation. This symposium provided one of
    the first opportunities for an international exchange of quite diverse
    opinions on the effects of microwaves. Recommendations adopted by the
    symposium included the promotion and coordination, at an international
    level, of research on the biological effects of microwaves, and the
    development of a non-ionizing programme by an international agency
    (Czerski et al., 1974a).

        The International Radiation Protection Association (IRPA) became
    responsible for these activities by forming a Working Group on
    Non-Ionizing Radiation at its meeting in Washington, DC, in 1974. This
    Working Group later became the International Non-Ionizing Radiation
    Committee (IRPA/INIRC) at the IRPA meeting in Paris in 1977 (IRPA,
    1977).

        Two WHO Collaborating Centres, the National Research Institute of
    Mother and Child, Warsaw (for Biological Effects of Non-Ionizing
    Radiation) and the Bureau of Radiological Health, Rockville (for the
    Standardization of Non-Ionizing Radiation) cooperated with the
    IRPA/INIRC in initiating the preparation of the criteria document. The
    final draft was prepared as a result of several working group
    meetings, taking into account comments received from the national
    focal points for the WHO Environmental Health Criteria Programme in
    Australia, Canada, Japan, Netherlands, New Zealand, Poland, Sweden,
    the United Kingdom, and the USA as well as from the United Nations
    Environment Programme, the United Nations Industrial Development
    Organization, the International Labour Organisation, the Food and
    Agriculture Organization of the United Nations, the United Nations
    Educational, Scientific and Cultural Organization, and the
    International Atomic Energy Agency. The collaboration of these

    national institutions and international organizations is gratefully
    acknowledged. Without their assistance this document could not have
    been completed. In particular, the Secretariat wishes to thank
    Professor P. Czerski, Mrs A. Duchne, Mr F. Harlen, Dr M. Repacholi,
    and Dr M. Shore for their help in the final scientific editing of the
    document.

        The document is based primarily on original publications listed in
    the reference section. Additional information was obtained from a
    number of general reviews, monographs and proceedings of symposia
    including: Gordon, 1966; Presman, 1968; Petrov, ed., 1970; Silverman
    et al., ed., 1970; Marha et al., 1971; Michaelson, 1977; Minin, 1974;
    Dumanski et al., 1975; Tyler, ed., 1975; Baranski & Czerski, 1976;
    Glaser & Brown, 1976; Glaser et al., 1976, 1977; IVA Committee, 1976;
    Johnson et al., 1976; Johnson & Shore, ed., 1977; Justesen & Guy,
    1977; Hazzard, ed., 1977; Serdjuk, 1977; Taylor & Cheung, ed., 1977;
    National Health and Welfare, Canada, 1977, 1978; Durney et al., 1978.

        Modern advances in science and technology change man's
    environment, introducing new factors which besides their intended
    beneficial uses may also have untoward side effects. Both the general
    public and health authorities are aware of the dangers of pollution by
    chemicals, ionizing radiation, and noise, and of the need to take
    appropriate steps for effective control. The increasing use of
    electrical and electronic devices, including the rapid growth of
    telecommunication systems (e.g., satellite systems),
    radiobroadcasting, television transmitters, and radar installations
    has increased the possibility of human exposure to electromagnetic
    energy and, at the same time, concern about possible health effects.

        This document provides information on the physical aspects of
    electromagnetic fields and radiowaves in the frequency range of 100
    kHz-300 GHz, which has been arbitrarily subdivided according to the
    traditional approach into microwaves (300 MHz to 300 GHz) and
    radiofrequencies (100 kHz to 300 MHz). A brief survey of man-made
    sources is presented. It is known that electromagnetic energy in this
    frequency range interacts with biological systems and a summary of
    knowledge on biological effects and health aspects has been included
    in the document. In a few countries, concern about occupational and
    public health aspects has led to the development of radiation
    protection guides and the establishment of exposure limits. Several
    countries are considering the introduction of recommendations or
    legislation concerned with protection against the untoward effects of
    non-ionizing energy in this frequency range. In others, the tendency
    is to revise existing standards and to adopt less divergent exposure
    limits. It is hoped that this criteria document may provide useful
    information for the development of national protection measures
    against non-ionizing radiation.

        Details of the WHO Environmental Health Criteria Programme,
    including some of the terms frequently used in the documents, can be
    found in the introduction to the environmental health criteria
    document on mercury (Environmental Health Criteria 1 - Mercury, World
    Health Organization, Geneva, 1976), now available as a reprint.

    1.  SUMMARY AND RECOMMENDATIONS FOR FURTHER STUDIES

    1.1  Summary

    1.1.1  Physical characteristics in relation to biological effects

        Microwave and radiofrequency (RF) radiation constitute part of the
    whole electromagnetic spectrum. This document is concerned with
    frequencies lying between 105 and 3  1011 Hz (100 kHz and
    300 GHz). The term radiofrequency refers to the range 100 kHz-300 MHz
    (3 km to 1 m wavelength in air) and microwaves to the frequency range
    of 300 MHz-300 GHz (1 m to 1 mm wavelength in air).

        Exposure conditions in the microwave range are usually described
    in terms of "power density" and are reported in most studies in watts
    per square metre, or milliwatts or microwatts per square centimetre
    (W/m2, mW/cm2, W/cm2). However, close to microwave and RF
    sources with longer wavelengths, the values of both the electric (V/m)
    and magnetic (A/m) field strengths provide a more appropriate
    description of the radiation. Exposure conditions can be altered
    considerably by the presence of objects, the degree of perturbation
    depending on their size, shape, orientation in the field, and
    electrical properties. Very complex field distributions can occur,
    both inside and outside biological systems exposed to microwaves and
    RF. Refraction of the radiation within these systems can focus the
    transmitted radiation resulting in markedly nonuniform fields and
    energy deposition. Different energy absorption rates may result in
    thermal gradients causing biological effects that may be generated
    locally, difficult to predict, and perhaps unique.

        When electromagnetic radiation passes from one medium to another,
    it can be reflected, refracted, transmitted, or absorbed, depending on
    the biological system and the frequency of the radiation. Absorbed
    microwave and RF energy can be converted to other forms of energy and
    cause interference with the functioning of the living system. Most of
    this energy is converted into heat. However, not all microwave and RF
    radiation effects can be explained in terms of the biophysical
    mechanisms of energy absorption and conversion to heat. It has been
    demonstrated both theoretically and experimentally that other types of
    energy conversion are possible. Interactions at the microscopic level
    leading to perturbations in complex macromolecular biological systems
    (cell membranes, subcellular structures) have been postulated.
    Biological phenomena caused by such perturbations are expected to show
    a resonant frequency dependence.

    1.1.2  Sources and control of exposure

        General population exposure from man-made sources of microwave and
    RF radiation now exceeds that from natural sources by many orders of
    magnitude. The rapid proliferation of such sources and the substantial

    increase in radiation levels is likely to produce "electromagnetic
    pollution". Major man-made sources include: radar installations,
    broadcasting and television networks, and telecommunication equipment.
    In industrial, commercial, and home equipment, notably those where
    energy is applied for heating purposes such as plastic sealing,
    welding, drying, cooking, and defrosting, there may be extraneous
    emission (leakage) of microwave or RF radiation.

        The problem of this extraneous radiation or pollution from sources
    of 100 kHz-300 GHz electromagnetic waves varies from country to
    country, depending on the degree of industrialization. Radiation
    emitted from high power sources such as broadcasting and
    telecommunication networks propagates over large distances and may
    even cover the whole circumference of the globe. With the increasing
    use of transmitter/receivers by sea and air traffic, and the necessity
    for ground-based radar control, increased levels of environmental
    electromagnetic radiation may constitute a problem in many countries.

        Problems of pollution range from electromagnetic interference,
    particularly in relation to the operation of health services, to
    direct risks to the health of individuals.

    1.1.3  Biological effects in experimental animals

        When sufficient microwave and RF radiation is absorbed and
    converted into heat there is a consequent rise in temperature in the
    organism. Injuries that have been studied in animals have resulted
    from exposure to high levels of radiation and have varied from local
    lesions and necrosis to gross thermal stress from hyperthermia. Death
    from hyperthermia was found to occur following exposure to power
    densities of a few tens of mW/cm2 to several hundreds of mW/cm2,
    depending mainly on the size of the animal and the radiation
    frequency. Recently, there has been a much wider appreciation of the
    consequences of nonuniform energy deposition (as described in sections
    6:3 and 7.1). Lesions have been found in the internal organs of
    animals exposed for prolonged periods during which there was no
    significant rise in rectal temperature. Furthermore, such animals did
    not show any overt signs of distress.

        Acute exposures may cause injury to the eye. The cornea and
    crystalline lens are particularly susceptible to injury within the
    frequency range of 1-300 GHz. The cornea is at greatest risk between
    10 and 300 GHz and the crystalline lens from 1 to 10 GHz. For
    short-terma exposures, the cataractogenic incident power density
    levels lie within the range of 150-200 mW/cm2. Cataract formation
    induced by a 1-h exposure can take as long as 10-14 days to develop.
    The formation of retinal lesions is also possible.

        It has been demonstrated that low-level,b long-terma exposure
    may induce effects in the nervous, haematopoietic, and immunocompetent
    cell systems of animals. Such effects have been reported in small
    animals (rodents) exposed to incident power density levels as low as
    0.1-1.0 mW/cm2. The reported effects on the nervous system include
    behavioural, bioelectrical, metabolic, and structural (at the cellular
    and subcellular levels) changes. Erythrocyte production and
    haemaglobin synthesis may be impaired and immunological reactivity
    changed. All these effects may influence the susceptibility of animals
    to other environmental factors. For example medium level, long-term
    exposure increases the sensitivity of animals to neurotropic drugs,
    particularly those inducing convulsions. Thermal mechanisms seem
    wholly inadequate to account for the results of studies indicating
    that cerebral tissue, exposed to weak electromagnetic fields, responds
    only over a limited range of intensities and modulation frequencies of
    the RF carrier field. There appears to be evidence for both amplitude
    and modulation frequency windows, outside which effects are not
    observed.

        Genetic effects, effects on development, and teratogenic effects
    have been observed in animals and plants. Numerous reports have
    indicated that at sufficiently high intensities, microwave and RF
    exposure may induce chromosomal aberrations, and also disturbances in
    somatic cell division (mitosis), germ cell maturation (meiosis), and
    spermatogenesis (section 7.7). The intensity levels required to
    produce these effects seem to indicate that a thermal mechanism may be
    responsible. Existing information on the influence of microwave and RF
    exposure on the transmission and expression of hereditary traits is,
    however, insufficient. No threshold levels or dose-effect
    relationships can be established at present.

    1.1.4  Power density ranges in relation to health effects

        During the 1973 Warsaw International Symposium on biological
    effects and health hazards of microwave radiation, it was agreed that
    microwave power densities could be divided into ranges. The following
    is an abridged version of this agreement:

        Microwave densities may be divided into the following 3 ranges:

        (a) High power densities, generally greater than 10 mW/cm2, at
    which distinct thermal effects (see Glossary) predominate;

             

    a  See Glossary.
    b  In this document, the ranges for low, medium, and high level
       exposures are approximately those agreed by the Warsaw symposium
       (section 1.1.4).

        (b) Medium power densities, between 1-10 mW/cm2, where weak but
    noticeable thermal effects exist; and

        (c) Low power densities, below 1 mW/cm2, where thermal effects
    are improbable, or at least do not predominate.

        The boundaries indicated for these ranges are arbitrary and depend
    on numerous factors, such as animal size, threshold of warmth
    sensation, frequency, and pulsing. The introduction of the
    intermediate range of subtle effects calls attention to the need for
    additional research, aimed at clarification of the underlying
    mechanisms.

        It should be noted that the classification applied to the
    microwave region (300 MHz-300 GHz). A similar classification was not
    determined for the RF region (100 kHz-300 MHz).

    1.1.5  Exposure effects in man

        The meagre evidence available on exposure effects in man has been
    obtained from incidents of accidental acute over-exposure to
    microwaves and RF. Not enough attention has been given to the conduct
    of epidemiological investigations. In some human studies, which have
    been conducted on people exposed occupationally, subjective symptoms
    have been reported.

        A considerable number of people in many countries have received
    microwave and RF diathermy treatment at power levels of several tens
    of watts for a duration of about 20 min daily over a period of some
    weeks.

        Adverse effects have not been adequately investigated among
    diathermy patients. This is a group of people exposed to microwaves
    and RF who can be readily identified and such studies should be
    carried out, as they may yield considerable information concerning
    exposure effects in man.

    1.1.6  Health risk evaluation as a basis for exposure limits

        Theoretical considerations, experimental animal studies, and
    limited human occupational exposure data constitute the basis for the
    establishment of health protection standards. It should be noted that,
    in some countries, microwave and RF health protection standards have
    recently been changed and that there is a tendency to adopt less
    divergent exposure limits in comparison with those proposed two
    decades ago.

        In establishing health protection standards, different approaches
    and philosophies have been adopted.

        A highly conservative approach would be to keep exposure limits
    close to natural background levels. However, this is not technically
    feasible. A reasonable risk-benefit analysis has to be considered.

        More data on the relationship between biological and health
    effects and the frequency and mode of generation of the radiation,
    particularly in complex modulations, are needed.

        In the case of pulse modulation, peak power density may be a
    factor which should be considered in setting exposure limits. However,
    it is not possible to propose a limit of peak power density from the
    information available at present.

    1.2  Recommendations for Further Studies, Exposure Limits, and
         Protective Measures

    1.2.1  General recommendations

        The basic biophysical mechanisms of interaction of microwaves and
    RF with living systems still need clarification and further studies.

        Work on both theoretical and experimental dosimetry, the
    calculation and measurement of fields and of energy deposited within
    simulated or actual biological systems, should be continued and
    refined.

        Results of animal studies are difficult to extrapolate to man, and
    these studies alone do not constitute a satisfactory basis for the
    establishment of health protection criteria. They should, therefore,
    be supplemented by appropriate epidemiological studies in man.

        The existing data on power, amplitude, and frequency "windows"
    seem to warrant continued investigations.

        The effects of chronic exposure on sensitivity to convulsant and
    other drugs are potentially useful and may have a direct bearing on
    the development of exposure standards.

        Long-term, low-level exposures combined with such stresses as high
    ambient temperature and humidity should be investigated.

        There is little published information on dose-effect
    relationships; reports tend to be limited to whether effects are
    observed at one particular level of exposure rather than over a range.
    More dose-related information, even covering small subject areas,
    would be valuable.

        Investigations on the genetic effects and effects on development
    of microwave and RF radiation should have priority.

        Attention should be given to investigating the different
    sensitivities to microwave/RF exposure of subgroups within the general
    population.

        National and international agreements on exposure limits, ways and
    means of controlling this type of environmental pollution, and
    concerted efforts to implement such agreements are needed.

    1.2.2  Measurement techniques

        There is a continuing need for the development of microwave/RF
    measuring instruments that: (a) give direct readings of electric or
    magnetic field strength, or power density; (b) are robust; (c) are
    portable, light-weight, and battery-operated; and (d) are sensitive
    and can be used over a wide frequency range.

        The problem of the design of personal dosimeters also remains to
    be solved.

    1.2.3  Safety procedures

        Computation techniques or methods that predict the distribution of
    fields close to deliberate high-power emitters (in the near field) are
    needed.

        Emphasis should be placed on the development of technology to
    ensure containment and limitation of radiation to the deliberately
    exposed object, as well as the reduction of leakage emission from
    devices.

        Personal protective devices should be used only as a last resort.

        Adequate medical surveillance of occupationally-exposed persons
    should be provided.

        Once exposure limits have been set, safety guidelines or codes of
    practice concerning safe use and installation design should be
    developed as soon as possible.

    1.2.4  Biological investigations

        Reports of experimental work should contain sufficient information
    describing the exposure conditions to allow an estimation not only of
    the total absorbed energy but also, as far as possible, of the
    distribution of the energy deposited within the irradiated biological
    system.

        Systematic investigation of the effects of microwave/RF exposure
    at all levels of biological organization are to be encouraged. This
    includes effects at the molecular level on subcellular components;

    cells, viruses, and bacteria; organs and tissues; and whole animals.
    Particular attention should be paid to: (a) long-term, low-level
    exposures and possible delayed effects; (b) the possibility of
    differences in sensitivity of various body organs and systems, where
    specific effects in various animal species are being considered; and
    (c) the influence of microwave/RF exposure on the course of various
    diseases, including any possible increase in sensitivity to
    microwaves/RF that may result because of the disease state.

    1.2.5  Epidemiological investigations

        Epidemiological studies should be carried out in a careful manner,
    paying attention to the relationship between exposure to microwaves/RF
    and other environmental factors occurring in the place of work and to
    the health status of the investigated group. Specific biological
    endpoints should be selected and adequate examination methods used for
    such studies. Conventional medical examinations will not provide
    sufficient information.

        Studies should be carried out on (a) workers occupationally
    exposed to microwave/RF sources; (b) patients treated with microwave
    and RF diathermy; and (c) groups within the general population living
    near high-power microwave/RF sources.

        A distinction should be made between occupational and public
    health protection standards.

    1.2.6  Exposure limits and emission standards

    1.2.6.1  Occupational exposure limits

        The occupationally-exposed population consists of healthy adults
    exposed under controlled conditions, who are aware of the occupational
    risk. The exposure of this population should be monitored.

        It is possible to indicate exposure limits from available
    information on biological effects, health effects, and risk
    evaluation. For occupational exposure, values within the range
    0.1-1 mW/cm2 include a high enough safety factor to allow continuous
    exposure to any part of the frequency range over the whole working
    day. Higher exposures may be permissible over part of the frequency
    range and for intermittent or occasional exposures. Special
    considerations may be indicated in the case of pregnant women.

    1.2.6.2  Exposure limits for the general population

        The general population includes persons of different age groups
    and different states of health, including pregnant women. The
    possibility that the developing fetus could be particularly
    susceptible to microwave/RF exposure deserves special consideration.

        Exposure of the general population should be kept as low as
    readily achievable and exposure limits should generally be lower than
    those for occupational exposure.

    1.2.6.3  Emission standards

        Emission standards for equipment should be derived from, and be
    lower than exposure limits, where this can reasonably be achieved. A
    class of equipment may be considered safe and exempt from regulations,
    if hazardous levels of radiation exposure cannot originate from such a
    source.

    1.2.6.4  Implementation of standards

        The implementation of microwave and RF occupational and public
    health protection standards necessitates: the allocation of
    responsibility for measurements of radiation intensity and
    interpretation of results; and the establishment of detailed radiation
    protection safety codes and guides for safe use, which indicate, where
    appropriate, ways and means of reducing exposure.

    1.2.6.5  Other protective measures

        Prevention of health hazards related to microwave and RF radiation
    also necessitates the establishment of rules for the prevention of
    interference with medical electronic equipment and devices such as
    cardiac pacemakers, prevention of detonation of electroexplosive
    devices, and prevention of fires and explosions due to the ignition of
    flammable material (vapours) by sparks originating from induced
    fields.

    1.2.6.6  Studies related to the establishment of limits

        Studies of the frequency and modulation dependence of biological
    and health effects are of prime importance. The results of such
    investigations may make it possible to modify the rationales of
    present day standards and to identify frequencies at which exposure
    limits should be lower or higher than those suggested in section 11.

    2.  MAGNITUDE OF EXPOSURE TO MICROWAVE AND RF RADIATION AND SOURCES OF
        CONCERN

        Electromagnetic fields and RF radiation occur naturally over a
    very wide range of frequencies. The ionosphere very effectively
    shields the earth's biosphere from radiations of this type originating
    in space. Electromagnetic fields and radiation of high intensity may
    be generated by natural electrical phenomena such as those
    accompanying thunderstorms.

        However, in the frequency range of 100 kHz to 300 GHz, the
    intensity of natural fields and radiation is low. Exposure of the
    urban population in the USA to man-made microwave sources was found by
    Janes (1979) to vary from a very low value to as high as 100 W/cm2.
    The median exposure to the total microwave flux from external sources
    for this population was calculated to be 0.005 W/cm2. Osepchuk
    (1979) has calculated the background exposure from the sun, integrated
    up to 300 GHz to be 1.4  10-5 W/cm2. These values can be put in
    better perspective by noting that the integrated microwave/RF flux
    emitted from the human body has been calculated by Justesen (1979) to
    be up to 0.5 W/cm2.

        The proliferation of man-made sources of energy in the 100 kHz-300
    GHz range has only occurred over the last few decades. From the point
    of view of biological evolution, this energy constitutes a very recent
    physical factor in the environment. Observations of biological effects
    from exposure to microwaves gave rise to concern in the early 1940s.
    On the basis of special research programmes, radiation protection
    guides recommending exposure limits were developed in the 1950s in the
    USSR and the USA. Thereafter, several industrialized countries
    introduced recommendations and/or legislation on microwave and RF
    health protection. It should be noted, however, that exposure limits
    vary widely, and are the subject of many discussions and much
    controversy.

        Although concern about microwave and RF effects and possible
    hazards arose first in highly developed countries, the problem is
    universal. Developing countries are rapidly establishing
    telecommunications, broadcasting systems, and other sources of
    electromagnetic energy. Electromagnetic waves emitted in particular
    countries may propagate around the globe. A report from the USA
    (Office of Telecommunications Policy, 1974) states: "Unless adequate
    monitoring programs and methods of control are instituted in the near
    future, man may soon enter an era of energy pollution comparable to
    that of chemical pollution of today."

        The urgent need for international agreement on maximum exposure
    limits and international programmes for the containment of
    electromagnetic pollution has been stressed at international meetings
    (Czerski et al., 1974a). Prevention of potential hazards is a more
    efficient and economical way of achieving control than belated efforts
    to reduce existing levels.

    3.  PROPERTIES OF MICROWAVE AND RADIOFREQUENCY (RF) RADIATION

        Radiowaves in the frequency range 100 kHz-300 GHz are non-ionizing
    electromagnetic radiation, and can be described in terms of
    time-varying electric and magnetic fields moving though space in
    wavelike patterns, as represented in Fig. 1.

        The wavelength (the distance between corresponding points of
    successive waves) and the frequency (the number of waves that pass a
    given point in 1 second) are related and determine the characteristics
    of electromagnetic radiation. The shorter the wavelength, the higher
    the frequency. At a given frequency, the wavelength depends on the
    velocity of propagation and therefore, will also depend on the
    properties of the medium through which the radiation passes. The
    wavelength normally quoted is that in a vacuum or air, the difference
    being insignificant. However, the wavelength can change significantly
    when the wave passes through other media. The linking parameter with
    frequency is the velocity of light (3  108 m/second in air). The
    velocity decreases and the wavelengths become correspondingly shorter,
    when microwaves and RF radiation enter biological media, especially
    those containing a large proportion of water.

        Another related property of electromagnetic waves is the photon
    energy, which increases linearly as the frequency increases. Fig. 2
    shows the spectrum of electromagnetic radiation ranging from highly
    energetic ionizing radiation with extremely high frequencies and short
    wavelengths to the less energetic non-ionizing radiation with the much
    lower frequencies and longer wavelengths of radio-frequencies.

        Conventionally a photon energy of 12eV, corresponding to a
    wavelength of 100 nm, is taken as the dividing line between ionizing
    and non-ionizing radiation. This is in the vacuum region of the
    ultraviolet spectrum. Microwave and RF radiations are much less
    energetic. Their energy per photon corresponds to 1.25  10-3 eV at
    300 GHz and 4.1  10-10 eV at 100 kHz, and is much too low to cause
    ionization.

    3.1  Units of Radiation

        When microwave or RF radiation is absorbed in a medium, the most
    obvious effect is heating. The radiation intensity can be determined
    calorimetrically. In SI terminology, it is known as the irradiance and
    is expressed in W/m2. Traditionally, however, the term "power
    density" has been and continues to be used for this part of the
    frequency range, and will be used in this document with the more
    commonly reported units of mW/cm2 and W/cm2.

    FIGURE 1

    FIGURE 2

        The associated electric and magnetic field strengths  (E and  H)
    can be equally valid expressions of radiant energy flow. When these
    are stated in V/m and A/m, respectively, their product yields VA/m2.
    At distances greater than about one wavelength from the source,
     E and  H are in phase and VA/m2 may be expressed as W/m2.
    Ideally, at a distance sufficiently remote from the source of
    radiation that it can be regarded as a point source, an inverse square
    law of power density with distance applies, the ratio  E/H is 120 pi,
    i.e., 377OMEGA. The power density can, therefore, be derived from
     E 2/377 or from  H 2  377. Where  E and  H are expressed in
    V/m and A/m (Table 1), this is referred to as plane-wave or far-field
    conditions and to obtain a measure of the radiated power density, only
    the  E field or the  H field need be measured. Most instruments used
    for measuring power density measure the  E field, because this
    technique is more versatile and presents fewer practical problems.  H
    field detectors have been devised for a limited range of frequencies.
    Instruments combining both types of detection are possible, in
    principle, but would be most difficult to construct.

    Table 1.  Comparison of power densities in the more commonly used
              units for free-space, far-field conditions
                                                                        

       W/m2      mW/cm2     W/cm2          V/m            A/m
                                                                        

       10-2       10-3         1           2              5 x 10-3
       10-1       10-2        10           6            1.5 x 10-2
        1         10-1        102          2 x 10         5 x 10-2
       10          1          103          6 x 10       1.5 x 10-1
       102        10          104          2 x 102        5 x 10-1
       103        102         105          6 x 102      1.5
       104        103         106          2 x 103        5
                                                                        


        The distance beyond which far-field conditions apply is usually
    taken as being 2 a 2/lambda, where  a is the maximum dimension of
    the source (antenna) and lambda is the wavelength. The radiated "near
    field" includes distances of less than 2 a 2/lambda, where the
    inverse square law with distance does not apply and the impedance in
    space (the ratio E/H) may differ from 377OMEGA. Close to the source,
    at distances less than lambda, reactive components of  E and  H
    become progressively more important. Instruments, calibrated in units
    of power density but based on the measurement of  E, for instance,
    will become increasingly inaccurate at close range. The instruments
    make valid measurements of the  E fields, but their scale indications
    in terms of power density no longer apply. These and allied
    considerations are also discussed in section 4.3.2.

    3.2  Other Physical Considerations

        A detailed analysis and interpretation of the perturbing effects
    of objects placed in the path of microwave or radiofrequency beams
    requires the solution of Maxwell's field equationsa for the
    appropriate boundary conditions. However, an important insight can be
    obtained by comparison with the shorter wavelength visible radiation,
    to which the same equations apply. The general laws of geometrical and
    physical optics remain valid: particularly the latter because of the
    wavelengths involved and because deliberate generators of microwaves
    and RF emit coherent radiation, i.e., the wave fronts are regular and
    radiated over a narrow band of frequencies at any one time. Radiation

              

    a  A set of four fundamental equations that describe all electric
       and magnetic fields. Their solution for real materials requires
       knowledge of the macroscopic electrical and magnetic properties of
       the materials.

    reflected into the path of the incident beam will form standing waves
    and, at a distance of a few wavelengths, diffraction effects can cause
    additive and subtractive interference. Both effects have been
    convincingly demonstrated by Beischer & Reno (1977) at 1 GHz with man
    as the perturbing influence. Diffraction and internal reflections can
    also take place when radiation penetrates heterogeneous materials such
    as body tissues, leading to markedly nonuniform internal fields and
    energy deposition. As in geometric optics, the combination of a high
    refractive index and convex body contours behaves like a strong convex
    lens focusing the penetrating radiation. Absorption and internal
    scattering will limit the extent of these effects. Without the
    absorption of energy to initiate some change, there cannot be any
    biological effects.

        Direct radiation is usually polarized, i.e., the  E and  H
    fields are oriented parallel to particular orthogonal planes or rotate
    in an ordered fashion. The plane of polarization of the reflected
    radiation will, thus, be changed complicating the measurement of the
    combined beams and investigation of the biological effects.
    Orientation with respect to the plane of polarization is important in
    some measuring instruments and in the distribution and total energy
    absorption in animals and in man. In some radar applications, typical
    equipment may emit pulses of 1 microsecond (s) with a pause between
    pulses of 1 millisecond (ms). This constitutes a factor of 103 in
    the values of instantaneous power radiated and deposited, and of 30 in
    the electric fields, compared with continuous wave (cw) generation at
    the same average power. Thus, instruments to be used in pulsed fields
    must have a wider dynamic range and more robust burn-out
    characteristics.

    4.  SOURCES AND CONDITIONS OF EXPOSURE

    4.1  Natural Background Sources

        Microwave and RF radiation occurs naturally, but the intensity of
    natural radiation in the range of 100 kHz-300 GHz is very low in
    comparison with the overall intensity of man-made radiation in this
    range, as shown in Fig. 3. The intensity of natural fields is mostly
    due to atmospheric electricity, which is static and has an electric
    field intensity of about 100 V/m (IVA Committee, 1976). This is known
    as the earth's electric and magnetic field. Radio emissions of the sun
    and stars, which are equivalent to about 10 pW/cm2 in the range of
    100 kHz to 300 GHz also contribute to natural radiation. Local
    disturbances leading to increased field intensities occur during
    thunderstorms. Electromagnetic fields with a very wide frequency range
    are created (atmospheric noise) with a maximum field intensity at
    about 10 kHz (Minin, 1974; IVA Committee, 1976).

        Artificial microwave and RF radiation constitutes a very recent
    environmental factor, dating back only a few decades. Depending on the
    frequency range, exposure from man-made sources of microwave and RF
    radiation may be many orders of magnitude higher than that from
    natural radiation and man as a species has had no opportunity to adapt
    to microwave and RF radiation at such environmental levels (Presman,
    1968).

        There exists a great diversity of man-made sources, both in
    respect of power output and the power densities that are generated,
    and the frequency range in which the sources operate. According to the
    use of the source, different segments of the general population are
    exposed in different ways. There are obvious differences, depending on
    the development of the country, between the average exposure of the
    general population, the exposure of inhabitants of urban
    industrialized areas, and the exposure of inhabitants of rural areas.
    There is also a risk of exposure to microwaves and RF in some
    occupations. In view of this, the discussion of man-made sources must
    include a description of exposure situations.

    4.2  Man-Made Sources

        Any appliance that generates electricity or is driven by an
    electric current generates electromagnetic fields. These propagate
    through space in the form of electromagnetic waves. Man-made microwave
    and RF sources may be broadly divided into 2 classes, i.e., deliberate
    emitters, and sources of unintentional, incidental radiation.

    FIGURE 3

    4.2.1  Deliberate emitters

        Deliberate emitters generally have a radiating element (antenna)
    designed to emit electromagnetic waves into the surrounding
    environment in a specified manner. The frequency, direction of
    propagation, and the point of origin are determined by the intended
    use of the equipment. Because of physical laws, and, in spite of the
    degree of perfection of the design of a deliberate emitter, some
    unintentional leakage, or stray radiation is always generated. This
    should be taken into account when evaluating a deliberate emitter as a
    radiation source.

        Unintentional radiation may occur in the form of broad-band noise
    or may be generated as discrete harmonics. In some instances, it is
    generated by sources that emit radiation outside the microwave and RF
    ranges. For example, while the intentional radiation of fluorescent
    light tubes lies in the visible light range, such tubes also generate
    very low levels of microwave and RF white noise (Mumford, 1949).

        Typical deliberate emitters include radiobroadcasting and
    television stations, radar installations, and electronic wireless
    communication systems. These sources can be classified in different
    ways and classifications may vary from country to country depending on
    attitudes towards possible environmental and health effects. When
    classified according to the nominal power output or the effective
    radiated power (ERP), such emitters may be divided into high, medium,
    and low power sources. Radar systems used for tracking and guiding
    purposes, as well as sources used in satellite systems are among the
    most powerful. It was reported in 1974 in the USA, that there were 20
    nonpulsed unclassified sources with average effective radiated power
    (ERP) ranging from 5 GW to 31.6 GW and one experimental source with an
    average ERP of 3.2 TW (3.2  1012W) (Hankin, 1974). All these
    sources were used in conjunction with satellite systems. A further 144
    sources had an average ERP of 1 MW or more. The twenty most powerful
    unclassified pulsed (radar) sources had average ERPs between 8.7 MW
    and 840 MW and peak ERPs ranging from 35.4 GW to 2.8 TW; 229
    unclassified pulsed sources had peak ERPs of 10 GW or more. This may
    be compared with television or amplitude modulation (AM) broadcasting
    stations in which the power of the transmitters is of the order of
    tens of kW (usually about 50 kW) or radio telephones (walkietalkies),
    in which ERPs may be of the order of a few watts or less.

        Another approach towards classification of sources is to examine
    the configuration of the radiated fields and their propagation in
    space. Directional radiating elements (antennae) generating intense
    focused beams and multidirectional, variously polarized antennae may
    be used. Taking into account the power of the transmitter and the type
    of the radiating element, the magnitude of distances (or zones) at
    which various intensities of radiation (power densities on strength of
     E or  H fields) occur can be computed. In this case, the

    classification of sources also depends on arbitrarily chosen levels of
    radiation intensity. This approach may be useful in the siting of
    sources and in establishing "safe", "hazardous", and "danger" zones
    around a source.

        Deliberate emitters may be also classified according to the mode
    of generation. Microwaves and RF may be generated continuously or in
    pulses and both continuous and pulsed wave generators may operate for
    long periods (up to 24 h per day) or short intermittent periods. The
    generated radiosignal may be frequency, amplitude, or pulse-modulated.
    Sources with moving directional antennae and sources generating mobile
    narrow beams may illuminate a point in space intermittently with a
    time-varying intensity ranging from zero to extremely high, at pulse
    peak power. Because of these complexities and since a point in space
    may be illuminated by radiation originating from several sources, the
    determination of the total or average quantity of energy delivered at
    this point during a period of time, may be difficult and may
    necessitate the use of sophisticated equipment and advanced computing
    methods.

        Evaluations of the intensity of microwave and RF radiation
    generated by deliberate emitters have been published in the USA (Smith
    & Brown, 1971; Tell, 1972; US Environmental Protection Agency, 1973;
    Tell & Nelson, 1974a; Tell et al., 1974; Hankin et al, 1976; Stuchly,
    1977; Tell & Janes, 1977; Tell & Mantiply, 1978). Fig. 4-7 illustrate
    the number of sources operating in the frequency range 10 kHz-300 GHz
    and capable of producing power densities equal to or greater than
    10 mW/cm2, 1 mW/cm2, 0.1 mW/cm2, and 0.01 mW/cm2. These data
    should be compared with data in Tables 2-6.

        Table 2 presents anticipated characteristics of satellite
    communications systems, which are among the most powerful sources of
    continuous wave radiations (100 W/m2, 10 W/m2, 1 W/m2, and
    0.1 W/m2). Table 3 presents characteristics of pulsed wave, high
    power generators, and Tables 4 and 5 include characteristics of
    on-board aircraft and marine radars, respectively. Table 6 shows the
    characteristics of some North American broadcasting transmitters, the
    electric field intensity, and the equivalent power density at ground
    level at a distance of one mile from the transmitter tower. Fig. 8
    presents power density versus distance for a television transmitter.
    In this context, it should be stressed that according to data of the
    US Environmental Protection Agency (Tell, 1972; Hankin et al., 1976;
    Tell & Mantiply, 1978) and the US Bureau of Radiological Health (Smith
    & Brown, 1971), broadcasting stations are "significant sources of RF
    exposure" (Tell & Janes, 1977). In view of the increasing popularity
    of mobile (portable or mounted on vehicles) transmitters for personal
    use, field intensities in the vicinity of antennae of these citizen
    band (CB) transmitters may be of concern in some countries from the
    point of view of population exposure (Neuksman, 1978; Ruggera, 1979).

    FIGURE 4

    FIGURE 5

    FIGURE 6

    FIGURE 7



        Table 2.  Anticipated characteristics of selected satellite communication systemsa
                                                                                                    

                                                                    Distance in km from antenna
                                                                      for power densities of
                                                                                                    

    System             f(GHz)     Pav(kW)    Pmax(mW/cm2)     0.1 mW/cm2      1 mW/cm2      10 mW/cm2
                                                                                                    

    LET                  8.1         2.5        30.4             0.246           0.78          2.46
    AN/TSC-54            8.1         8          50.8             0.46            1.45          4.58
    AN/FSC-9             8.1        20           7.6             6.23           19.7          62.3
    Intensat             6.25        5           0.73             --              --          12.3
    Goldstone Venus      2.38      450          97.3             4.16           13.2          41.6
    Goldstone Mars       2.38      450          16.8             9.68           33.4         106
                                                                                                    

    a  From: National Health and Welfare, Canada (1977) based on Hankin et al. (1976).

    Table 3.  Anticipated characteristics of typical high peak power radarsa
                                                                                                      

                                                                      Distance in km from antenna
                                                                         for power densities of
                                                                                                      
    System                f(GHz)      P(kW)      Pmax(mW/cm2)    10 mW/cm2     1 mW/cm2      0.1 mW/cm2
                                                                                                      

    Acquisition radar
      FPN -- 40            9.0          0.18         12.8          0.028         0.111         0.351
    Acquisition radar
      ARSR                 1.335       20           111            0.147         0.465         1.47
    Tracking radar
      Hawk Hi Power        9.8          4.7         800            0.108         0.344         1.08
    Tracking radar
      no. 1                2.85        12            34.2          9.392         1.24          3.93
    Tracking radar
      no. 2                1.30       150            55.7          1.75          5.52         17.5
                                                                                                      

    a  From: National Health and Welfare, Canada (1977) based on Hankin et al. (1976).

    Table 4.  Experimental data for typical on-board aircraft radarsa
                                                                                                       

                                                                               Approximate distance from
                                                   Power          Power           radome in m for power
    Radar               Aircraft       f(GHz)     average        density              density of
    system                                          (w)           max.                                 
                                                                (mw/cm2)       10 mW/cm2     1 mW/cm2
                                                                                                       

    WP       103      BAC 111          9.375         26            20             3                11
    AVQ       20      Convair          9.375         16            10             2                11
    AVQ       50      Convair 580      9.375         16            26             2                11
    AVQ       20      DC-9             9.375         28            15             4                13
                                                                                                       

    a  From: National Health and Welfare, Canada (1977) based on Tell & Nelson (1974a).


    Table 5.  Power density in the vicinity of on-board marine radars (non-rotating antennae)a
                                                                                                   

                                                                Distance       Average power density
                                                   Power          from                (W/cm2)
    System              f(GHz)         Peak       Average        antenna                           
                                       (kW)         (w)            (m)
                                                                                                   

    Decca 101           9.445            3          3.25           25.5         6.8      7.5  5.4
    Decca 202           9.445            3          1.5            45.7         3.6      5.1  4.6
    Decca RM316         9.41            10          5             103.6         3.7      5.9  5.0
    Kelvin-Hughes 17    9.445            3          2.75          103.6         0.6      1.4
    Konel KRA 221       9.375           10          4.8            45.7         9.2      6.1  4.5
                                                                                                   

    a  From: National Health and Welfare, Canada (1977), based on Peak at al. (1975).
    

    FIGURE 8



        Table 6.  Parameters of broadcasting transmittersa
                                                                                      

                        Frequency    Maximum        Tower         Field        Power
    Service               (MHz)        ERP         Height       intensity     density
                                      (kW)           (m)         (mV/m)      (W/cm2)
                                                                                      

    FM Radio             88--108       100           152          1023          2.78
    VHF-TV, ch. 2--6     54--88        100           305           807          1.73
    VHF-TV, ch. 7--13   174--216       316           305           191          0.1
    UHF-TV              470--890      5000           305           380          0.38
                                                                                      

    a  From: National Health and Welfare, Canada (1977), based on Tell (1972).
    

        Medical microwave and RF equipment (chiefly medical diathermy) is
    a particular class of deliberate emitters designed and used for the
    irradiation of human subjects to obtain beneficial effects. In this
    case, the intended human exposure is carried out under professional
    supervision and constitutes part of medical practice. The contribution
    of medical uses to the general population exposure is difficult to
    evaluate and varies from country to country. A survey in Pinellas
    County (Florida, USA) revealed that among a population of 500 000
    persons, 7037 individuals received 45 000 microwave or shortwave
    diathermy treatments of various durations and exposure levels (Remark,
    1971). It should be pointed out that the county has a large population
    of retired people.

        Although individual patients may absorb large quantities of
    energy, the exposure is limited to selected body areas and limited in
    time. However, medical microwave and RF equipment is also a source of
    unintentional radiation (Bassen et al, 1979) and during irradiation
    sessions, considerable scattering of electromagnetic fields may occur
    (Witters & Kantor, 1978; Bassen et al., 1979). Thus, particular
    attention should be paid to limiting exposure to the areas intended
    and to avoiding additional radiation doses to the patient from
    adjacent sources (other diathermy equipment). The occupational
    exposure of personnel operating the equipment should also be limited.
    The unintentional exposure of both patient and personnel usually
    involves the whole body.

    4.2.2  Sources of unintentional radiation

        Electrical and electronic, industrial or commercial equipment and
    consumer products in which, by design, the electromagnetic energy is
    contained within a restricted area, but into which objects to be
    processed are introduced, can all be sources of unintentional
    radiation. Any energy (radiation) emanating outside the area
    represents an energy loss. However, complete containment of
    electromagnetic energy is not always technically feasible. A typical
    example of a source of unintentional or leakage radiation is the
    microwave oven for commercial or home use. The microwave energy should
    be totally contained in the oven's cavity and used for heating
    (cooking) food. Leakage of microwaves does not serve any purpose and,
    if excessive, may represent a hazard to the user.

        Microwave and RF equipment is used in many industries for such
    processes as melting, welding, drying, gluing, plastic processing, and
    sterilization. Surveys of dielectric radiofrequency heaters in Canada
    (Stuchly et al., 1980; National Health and Welfare, Canada, 1980) have
    shown that these heaters are used predominantly for plastic sealing
    and wood gluing, and operate at frequencies between 4 and 51 MHz with
    output powers in the range of 0.5-90 kW. Operators of some of these
    devices were exposed to fields with equivalent power densities
    exceeding 10 mW/cm2. Most industries use electrical and electronic
    equipment (NIOSH, 1973). Table 7 represents various uses of microwave
    and RF generating equipment within certain frequency bands. Table 8
    shows frequencies allocated for industrial, scientific, and medical
    uses (ISM bands) and Table 9, the frequencies allocated for these
    purposes in the USA and the USSR.

        Unintentional exposure to microwave and RF radiations from
    deliberate emitters occurs universally. The results of a series of
    investigations by the US Environmental Protection Agency (section
    4.2.1) indicate that urban populations in highly industrialized
    countries may be exposed to overall intensities of the order of
    W/cm2 (Gordon, 1966; Marha et al., 1971; Minin, 1974; Dumanski et
    al., 1975; Baranski & Czerski, 1976; Johnson et al., 1976; IVA
    Committee, 1976; National Health and Welfare, Canada, 1977, 1978;
    Durney et al., 1978). Inhabitants of high buildings in the vicinity of
    the rooftop antennae of broadcasting and television stations may be
    exposed to levels ranging from a few hundred W to a few mW per cm2.
    According to Tell & Mantiply (1978), 50% of the urban population of
    the USA is exposed to less than 0.005 mW/cm2, 95% to less than 0.01
    mW/cm2, and 99% to less than 0.1 mW/cm2.

        Table 7.  Selected examples of the typical uses of equipment generating radiofrequency
              and microwave radiation
                                                                                                

    Frequency        Use                                     Occupational exposure
                                                                                                

    Below 3 MHz      Metallurgy: eddy current melting,       Metal workers; radiotransmitter
                     tempering; broadcasting,                personnel.
                     radiocommunications, radio-
                     navigation.

    3--30 MHz        Many industries such as the             Various factory workers, e.g.,
                     car, wood, chemical, and food           furniture veneering operators,
                     industries for heating,                 plastic sealer operators, drug &
                     drying, welding, gluing,                food sterilizers, car industry
                     polymerization, and sterilization of    workers; medical personnel;
                     dielectrics; agriculture; food          broadcasting transmitter and
                     processing; medicine; radio-            television personnel.
                     astronomy; broadcasting.

    30--300 MHz      Many industries as above; medicine;     Various factory workers, as above;
                     broadcasting, television,               medical personnel; broadcasting
                     air traffic control, radar              transmitter and television
                     radionavigation.                        personnel.

    300--3000 MHz    TV, radar (troposcatter and             Microwave testers; diathermy and
                     meteorological); microwave              microwave diathermy operators
                     point-to-point; telecommunication       and maintenance workers; medical
                     telemetry; medicine; microwave          personnel; broadcasting transmitter
                     ovens; food industry; plastic           and television personnel;
                     preheating.                             electronic engineers and technician:
                                                             air crews; missile launchers;
                                                             radar mechanics and operators
                                                             and maintenance workers.

    3--30 GHz        Altimeters; air- and ship-borne         Scientists including physicists;
                     radar; navigation; satellite            microwave development workers;
                     communication microwave point-to-       radar operators; marine and
                     point.                                  coastguard personnel; sailors,
                                                             fishermen and persons working on
                                                             board ships.

    30-300 GHz       Radiometeorology; space                 Scientists including physicists;
                     research; nuclear physics and           microwave development workers;
                     techniques; radio spectroscopy.         radar operators.
                                                                                                
    
        Table 8.  Designation and use of microwave and RF Bands
                                                                                             

      Letter designation of microwave frequency       Some industrial, scientific, and medical
                        bands                         (ISM) frequency bands, (not applicable
                                                               in all countries)
              Band           Frequency -- MHZ
                                                                                             

              L                1100--  1700                    13.56 MHz  6.78 kHz
              LS               1700--  2600                    27.12 MHz   160 kHz
              S                2600--  3950                    40.68 MHz    20 kHz
              C                3950--  5850                      433 MHz    15 MHz
              XN               5850--  8200                      915 MHz    25 MHz
              X                8200--12 400                     2450 MHz    50 MHz
              Ku             12 400--18 000                     5800 MHz    75 MHz
              K              18 000--26 500                   22 125 MHz   125 MHz
              Ka             26 500--40 000
                                                                                             
    

        General population exposure may be considered as long-term, very
    low-level, intermittent exposure for 24 h per day (or for major
    portions of the day) to a very wide range of microwave and RF
    radiation frequencies.

    4.3  Estimating Exposure Levels

    4.3.1  Far-field exposure

        Estimates of far-field exposures are necessary before powerful and
    complex installations are constructed. The subject is discussed at
    length by Minin (1974), who not only considers factors connected with
    equipment and the local topography but also gives information on
    methods of screening. Whenever possible, estimates of radiation fields
    should be made before detailed surveys of potentially hazardous
    exposures are carried out. Mumford (1961) gives approximate formulae
    for some radar antennae; additional information can be obtained from
    textbooks and monographs (Kulinkovskaja, 1970; ANSI, 1973; US
    Department of Commerce, 1976; National Health and Welfare, Canada,
    1977; Krylov & Jucenkova, 1979). This procedure is necessary not only
    to select a suitable survey instrument but also to determine if
    potentially hazardous exposure of the operator could occur, if the
    instrument were faulty. Unlike instruments for ionizing radiation,
    there are no sources readily available for checking the calibration of
    the instrument.


        Table 9.  Radiofrequency and microwave band designations
                                                                                                            

    Band designations
                                
         USA            USSR
                                                                                                            

     (a) Radiofrequency bends

    Low frequency       (LF) Long      VCh       104-103 m    30-3 kHz      radionavigation; radio
                                                                            beacon AM broadcast.

    Medium              Medium         (HF)      103-102 m    0.3-3 MHz     marine radiotelephone;
    frequency (MF)                                                          AM broadcasting.

    High frequency      (HF) Short     UHF       102-10 m     3-30 MHz      amateur radio; citizens band
                                                                            in the USA. etc.; world-wide
                                                                            broadcasting; medical diathermy;
                                                                            RF sealers, welders, heaters;
                                                                            short-wave diathermy.

    Very high           Ultra-short              10-1 m       30-300 MHz    Frequence modulated (FM)
    frequency (VHF)     (metre)                                             broadcasting; television; air
                                                                            traffic control; radionavigation.
                                                                                                            

     (b) Microwave bands

    Ultra high          Decimetre      Super                  0.3-3 GHz     microwave diathermy; television;
    frequency (UHF)                    HF                                   microwave point-to-point;
                                                                            microwave ovens & heaters;
                                                                            telemetry; tropo scatter &
                                                                            meteorological radar.
                                                                            
                                                                                                            

    Table 9 (Cont'd)
                                                                                                            

    Band designations
                                
         USA            USSR
                                                                                                            


    Super high          Centimetre     (SHF)     10-1 cm      3-30 GHz      satellite communication; air-
    frequency (SHF)                                                         borne weather radar; altimeters;
                                                                            shipborne navigational radar;
                                                                            microwave point-to-point;
                                                                            amateur radio.

    Extra high          Millimetre               1-0.1 cm     30 GHz-       cloud detection radar.
    frequency (EHF)                                           300 GHz
                                                                                                            
    

        In the far field on the antenna axis, power density (Pd) can be
    calculated from the formula:

         Pd =  GPt/ 4pi d2 =  AeP/lambda2 d2

    where  G is the far-field gain,  Pt is the power delivered to the
    antenna (W),  d is the distance from the antenna (m), lambda is the
    wavelength (m) and Ae is the effective area of the antenna (m2).
     G, the far-field gain of the antenna, represents the ratio of the
    observed power density, on axis, to the power density from a point
    source having the same output power and emitting equally in all
    directions.

    4.3.2  Near-field exposure

        When the distance is not great compared with the antenna
    dimensions, the power density tends to vary inversely with  d instead
    of  d2 (as in the far field), and may display interference
    patterns. Radiations from different parts of the antenna, having the
    same wavelength, combine in various phases. For parabolic antennae,
    the maximum power density ( P d) expected in the radiated near
    field can be estimated from:

         Pd = 4 Pt/ Ae

    where  Pt is the transmitted power and  Ae is the effective
    area of the antenna. This expression will generally overestimate the
    power density. A fuller discussion of this relationship is provided by
    Hansen (1976) and Hankin et al. (1976).

        Effects of ground reflections could increase  Pd by a factor
    of 4 or even more if focusing effects are present. These predicted
    values of maximum power density should be within 3 dB (i.e., within a
    factor of the true maxima for most horn antennae and circular
    reflector antennae). However, different antenna illumination functions
    may produce near-field power densities that may be higher than those
    predicted. It should be recognized that the equation is only suitable
    for obtaining approximate power densities to use as a rough guide.
    More precise values require careful measurements (Bowman, 1970, 1974;
    Ruggera, 1977).

        In the case of low frequencies or large aperture antennae, the
    existence of potentially hazardous reactive near fields becomes
    relevant. These electric and magnetic fields are calculable only with
    reference to the geometry of the specific antenna and source. For
    instance, exact equations for the electric and magnetic fields
    generated by a small electric dipole contain terms in
    lambda/ d,lambda/ d2, and lambda/ d3. When  d is much
    smaller than lambda, the lambda/ d3 terms predominate and this is
    referred to as the reactive near field. Objects within this region may

    couple with the source and extract energy. When lambda/ d approaches
    1, all terms contribute and this is sometimes called the intermediate
    field. When lambda/ d is substantially less than 1, the conditions
    are those of the far field.

    4.4  Facilities for Controlled Exposure

        Controlled exposure facilities are required for the calibration of
    instruments used in measuring power density, for the exposure of
    experimental animals in the study of effects, and for the exposure of
    phantoms (models) and carcasses in studies on absorbed energy and its
    distribution. The unrepeatability of much of the early biological work
    has been ascribed to the inadequacy of exposure facilities. Large
    gradients in field intensities are very undesirable and preferred
    methods make use of either far-field exposures carried out under
    conditions in which reflections are reduced to a minimum (e.g., in
    anechoic chambers), or using guided wave techniques. The basic premise
    is that known exposure conditions can be established by a combination
    of measurement and calculation. Except in laboratories with a
    responsibility for maintaining primary standards, it is probably
    preferable to use the far-field or guided wave methods to obtain
    suitable exposure conditions, and to measure the radiation field using
    an instrument that has been calibrated at a primary laboratory.

        The methods of instrument calibration have been described in
    detail by Engen (1973), Baird (1974), and Bassen & Herman (1977) and
    are summarized in the following section. The principles apply equally
    to animal exposure.

    4.4.1  Free space standard field method

        There are several variations of this method, but the objective is
    always to establish a known calibration field in free space. The most
    common experimental arrangement is shown in Fig. 9. As discussed in
    section 4.3.1, the power density ( P d) at a point on the
    transmitting antenna is given by:

         Pd =  GP t/4pi d2

        where  Pt is the power delivered to the transmitting antenna,
     G is the effective gain of the transmitting antenna, and  d is the
    distance from the antenna. The gain is normally determined in advance,
    and  Pt and  d are measured as part of the regular calibration
    procedure.

        The most convenient method of determining  Pt is by sampling
    forward or incident and reflected powers. The incident power  Pi
    and the reflected power  Pr are monitored, and  Pt is obtained
    from the relation  Pt =  Pi -  Pr. The high quality,
    broadband equipment available together with methods for its use in
    FIGURE 9

    determining  P i are described in Bramall (1971), Engen (1971),
    Aslan (1972), and Bowman (1976). The methods cited are for calibrating
    power meters, but the same techniques can be applied for the
    calibration of antennae, if corrections are made for mismatch effects,
    including those from animal exposure.

        The principal sources of error in the free space method are
    multipath interference and uncertainties in the determination of gain.
    Multipath effects have often been overlooked, but every calibrating
    facility will have some reflections associated with the walls,
    equipment, and probe support structure. These reflections may cause
    the field in the calibrating region to be significantly different from
    that predicted. Even high-quality anechoic chambers are not perfect
    and should be evaluated, if the greatest accuracy is desired.
    Calibration errors due to multipath effects can be reduced by
    observing the probe response as a function of position and averaging
    the results. This is sometimes referred to as the multiple position
    averaging technique and useful discussions of the method can be found
    in Bowman (1974), Bassen & Herman (1977), Swicord & Cheung (1977), and
    Swicord et al. (1977).

    4.4.2  Guided wave methods

        The fields inside a waveguide can be accurately calculated and, in
    some cases, are sufficiently uniform to be considered for calibration
    purposes (Hudson, 1966; Hudson & Saulsbury, 1971). The main advantage
    of such a system is that it requires considerably less power and
    space. One disadvantage is that the maximum transverse dimension of a
    rectangular waveguide must be less than the free space wavelength of
    the highest calibration frequency, in order to avoid higher order
    modes which result in complicated field distributions. Thus, the
    method is generally used for frequencies below 2.6 GHz, since the
    device being calibrated must be small compared with the guide
    dimension.

        The probe to be calibrated is usually inserted into the wave-guide
    through a hole in the side wall and positioned in the centre of the
    guide, where the field in most nearly uniform. It is difficult to
    estimate the total uncertainty of this method, because the field
    intensity will be modified by the size and nature of the probe being
    calibrated. A careful error analysis of this problem has not been
    completed, but it appears that, if the maximum probe dimension is less
    than one third of the smaller waveguide dimension, the total
    uncertainty should not exceed  1 dB (22%). Woods (1969) described a
    system which operated from 400 to 600 MHz with an estimated
    uncertainty in the field intensity of  0.5 dB (12%). Later results at
    2450 MHz have been reported by Aslan (1972) with claims of higher
    accuracy.

        Other types of guided wave structures can be used reliably to
    establish uniform fields for calibration purposes in the RF frequency
    range below about 500 MHz, where free space techniques become
    difficult and standard waveguides are unavailable or inconvenient. The
    two most commonly used structures are the parallel plane line and the
    Transverse Electromagnetic Mode (TEM) cell (Crawford, 1974). Both
    structures can be used to produce transverse electromagnetic waves
    with the same wave impedance (377OMEGA) as a plane wave in free space,
    a feature which makes them desirable for calibration purposes.
    Furthermore, the fields can be calculated with sufficient accuracy for
    many calibration purposes.

        A basic TEM cell is illustrated in Fig. 10. The principal
    advantage of this structure over the parallel plane line is that the
    TEM cell is fully shielded, thus eliminating extraneous radiation that
    may interfere with electronic equipment. The basic unit is a section
    of two conductor transmission lines. As shown in the figure, the main
    body of the cell consists of a rectangular outer conductor and a flat
    centre conductor located midway between the top and bottom walls. The
    field intensity in the centre of the cell can be quite uniform, and
    the wave impedance throughout the cell is very close to the free space
    wave impedance. It is mainly because of these features that this type
    of cell is used for calibrations.

        The dimensions of such a cell are adjusted according to the
    desired upper frequency limit.

    4.4.3  Standard probe method

        A stable and reliable probe, which has been accurately calibrated
    by one of the previously described techniques, a "transfer standard",
    is used to measure the field intensity over a particular region in
    space (or in a guided system) produced by an arbitrary transmitting
    antenna. The probe to be calibrated is then placed in the same
    location in the field and the meter reading compared with the known
    value of the field. The only requirements are that the transmitter
    should generate a field which has the desired magnitude, is constant
    in time, and is sufficiently uniform over the calibrating region.
    Accuracies of about  0.5 dB (12%) should be attainable. This method
    is the simplest, and may ultimately prove to be the best method of
    calibrating hazard meters for general field use Baird (1974). The
    advantages of this method are its convenience, reliability, and
    simplicity. Potential sources of error, when using the transfer
    standard to calibrate another probe, are the possible differences in
    the receiving patterns of the two probes, especially in the near
    fields of a source of radiation, and the errors due to scattering from
    probes under test.

    FIGURE 10

    5.  MEASURING INSTRUMENTS

    5.1  General Principles

        Most power density instruments are composed of 3 basic parts: the
    sensor, connecting leads, and meter unit. This configuration reduces
    perturbation of the field in the immediate vicinity of the sensor to a
    minimum and, in surveys of potentially hazardous equipment, may help
    in reducing the exposure of the operator. Neither leads nor meter unit
    should respond to the radiation being measured or serious error can
    ensue. The instrument should respond only to microwave and RF fields
    and not, for instance, to light and infrared radiation, or to static
    and low-frequency electric and magnetic fields. Comparatively few
    instruments are likely to meet these requirements in full.

        The basic principles of instrument calibration with the
    uncertainties associated with the different methods have already been
    discussed in section 4.4. The same accuracy cannot be expected or
    achieved when using the meters for making practical measurements in
    surveys because: (a) hazard meters are usually calibrated in nominally
    plane-wave fields, which are seldom encountered in practice, and the
    sensor may not respond in the same way to non-planar fields; and (b)
    in most calibration methods, only the sensor (probe) is exposed to the
    field, while, in practice, the complete system, including the
    indicating unit and connecting cable, is immersed in the field. Even
    when these do not respond to the radiation, the radiation fields will
    be perturbed by their presence and that of the operator. If good
    measurement procedures are followed, accuracies of 2 dB can be
    achieved.

    5.2  Types of Instruments in Common Use

    5.2.1  Diode rectifier

        In these instruments, small antennae terminate in single or
    multiple diodes. Multiple diodes and antenna elements arranged in
    suitable configurations can be used to sum all electric field
    components enabling measurements to be made, irrespective of
    polarization and direction of incidence. Three orthogonal elements are
    necessary and sufficient for such an isotropic instrument.

        Some units, now in use, employ a single diode combined with a
    short dipole or small loop antenna. The sensitivity of these
    instruments changes with their orientation, with respect to the plane
    of polarization of the  E or  H field. They must, therefore, be
    oriented so that the maximum value can be read -- a process that can
    be tedious and time-consuming. Such instruments are, however, useful
    for identifying and measuring individual field components.

        An orthogonal dipole array or multiple diodes and dipoles arranged
    in a single plane will respond well to all signals polarized in the
    plane of the array, but not to components polarized at wide angles to
    the array. Such units must also be oriented to obtain the maximum
    field readings.

        All these instruments are basically power density sensitive in the
    far field, that is, at low levels, the rectified voltages are
    proportional to the square of the  E field (i.e., to the power
    density). When adapted to broadband operation, the upper frequency
    range is, at present, about 18 GHz. The corresponding low frequency
    limit is about 0.5 MHz.

        Diode characteristics depend directly on ambient temperature and
    variations in output with ambient temperature may be in the order of
    tenths of a dB (several percent) per degree Celsius. Diode units may
    also be modulation sensitive, with errors in reading dependent on the
    form of modulation.

    5.2.2  Bolometer

        In bolometric instruments, the microwave/RF currents cause heating
    and induce a change in some physical property, most commonly the
    resistance of a thermistor. A measure of the power density would then
    be the resulting imbalance of a bridge circuit containing the
    thermistor. For small deviations from balance, the bridge output is
    proportional to the temperature of the thermistor and therefore to the
    square of the electric field, i.e., to the RF power dissipated in the
    thermistor. The thermistors used have a positive temperature
    coefficient. Thus, this type of instrument can withstand large
    overloads without damage. As the power density increases, the
    resistance of the element increases, causing a mismatch condition and
    the power absorbed by the thermistor is also inversely proportional to
    its resistance. Both effects limit the power absorbed by the element.
    These units may exhibit drift in the zero reading and loss in
    sensitivity caused by changes in ambient temperatures.

    5.2.3  Thermocouple

        The detection elements in thermocouple-type radiation monitors are
    generally thin-film type thermocouples. The films perform the
    simultaneous functions of lossy antenna element and temperature
    detector. The output from the thermocouple is proportional to the
    square of the electric field and the units are relatively independent
    of ambient temperature (Bassen et al., 1977). Hot and cold junctions
    of the thermocouple are in extremely close proximity and very stable.
    Variation in sensitivity is of the order of 0.1% perC. The use of
    small, thin, resistive films provides very broad bandwidth. More
    detailed discussions of these, and other types of instruments, can be
    found in Aslan (1972), Bowman (1976), Eggert & Goltz (1976), and
    Eggert et al. (1979).

    6.  MICROWAVE AND RF ENERGY ABSORPTION IN BIOLOGICAL SYSTEMS

        Electric and magnetic fields are induced within a biological
    system exposed to microwave or RF energy. To understand the resulting
    biological effects, it is necessary to determine the induced field
    strength at various internal points of the system. Knowing the
    electrical and geometrical characteristics of the irradiated object
    and the external exposure conditions, it is possible, in principle, to
    calculate the rate at which energy is absorbed throughout the interior
    of the irradiated object.

        The magnitude of interior and exterior scattered and reflected
    fields depends on many factors: the frequency and configuration of the
    incident field; the electrical properties of the various layers
    (tissues) of which the irradiated system is composed; the shape, the
    size relative to wavelength, and the relative orientation of the
    system. Biological systems are usually of complex exterior and
    interior geometry, and consist of several layers with various
    electrical properties (complex permittivity). As a result, the
    internal energy deposition in biological systems will be nonuniform.
    Depending on the thermal properties and blood flow of tissues, there
    can be marked differences in the magnitude and rate of increase in
    temperature, and thermal gradients can result. A review on the
    interaction of microwave and RF radiation with living systems has
    recently been completed by Stuchley (1979).

    6.1  Methods of Computation

        Methods of computation for predicting internal energy deposition
    using various approximate mathematical models of human and animal
    bodies have been developed. These show reasonable agreement with
    experimental measurements of energy absorption in phantom models and
    animal carcasses (Guy, 1971, 1974; Johnson & Guy, 1972).

        Theoretical analyses have led to the prediction of the resonant
    absorption of energy in both the whole and parts of the body of human
    models and animals. The effects of such variables as frequency and
    polarization of the field, the size and shape of the exposed body, and
    the surrounding environment, ground plane, and other objects have been
    evaluated.

        Details concerning computational and experimental techniques, data
    on specific absorption rates within the range of 10 kHz-100 GHz in man
    and laboratory animals, as well as pertinent reference lists, can be
    found in the three editions of the "Radiofrequency radiation dosimetry
    handbook" (Johnson et al., 1976; Durney et al., 1978, 1980). In the
    most recent edition of the Handbook, several models relevant to
    exposures in the near-field of the radiation source have been
    included.

        The intensity of the internal electric field or the amount of
    energy absorbed per unit time per unit mass (the specific absorption
    rate (SAR)) are both used in radio-frequency and microwave dosimetry.
    Most frequently used units of SAR are W/kg and mW/g. Further
    discussion on SAR follows in section 6.3.

    6.2  Experimental Methods

        Measurements of internal electric fields within dielectric media
    are possible if a small, insulated dipole array is used. Such a device
    has been developed in miniature form and used to measure internal
    microwave fields in phantoms and living animals with uncertainties of
    less, than 1 dB. The advantage of the implantable electric field probe
    method over thermal dosimetric techniques is the greater sensitivity
    of the field probe, allowing the use of microwave and RF sources with
    much lower power outputs. Thus, the energy deposition can be mapped in
    a biological body or a scan through a phantom exposed to only moderate
    levels of microwave or RF energy.

        Thermal measurements in phantoms or animal carcasses can yield
    direct data on SAR. Small thermistor probes with non-perturbing
    resistive leads, and optical fibre probes with temperature-sensitive
    sensors using a light source have been developed (Aslan, 1972; Cetas,
    1975; Livingston et al., 1975; Bowman 1976; Deficis & Prou, 1976;
    Bassen et al., 1977). Thermographic cameras used in conjunction with
    sectioned phantom models or carcasses can record the heat distribution
    in an entire plane. High intensity exposure fields have to be employed
    to yield significant increases in temperature.

    6.3  Energy Absorption

        Biological systems are lossy dielectrics characterized by limited
    conductivity. The losses originate from the movement of free ions
    (conduction loss) and molecular rotation (dielectric loss). Thus,
    electromagnetic waves, propagating through a biological medium,
    interact with it, and energy transfer occurs. This results in
    attenuation of the field and an increase in the kinetic energy of the
    molecules of the medium, i.e., in heating. The degree of attenuation
    of the field depends on the dielectric properties of the medium, and
    these change with the frequency of the incident field. The real and
    imaginary parts of the complex permittivity generally decrease with
    increasing frequency.

        The above statements present, in a simplified form, the classical
    theory of microwave and RF energy absorption, which was developed by
    Schwan and his school (Schwan & Piersol, 1954, 1955; Schwan, 1971,
    1976). The latest restatement of this approach (Schwan, 1978) may be
    summarized as follows: "Among the established effects in biological
    systems the most important is heat development but direct field

    interactions with membranes, biopolymers, and biological fluids are
    all possible". All energy deposition, however, takes place because of
    conduction losses, molecular movements, and biopolymer rotation.

        During the last few years, the concept of the specific absorption
    rate (SAR) has been developed for quantifying microwave and RF
    effects.

        As mentioned earlier, the specific absorption rate is defined as
    the rate of energy absorption per unit mass of an exposed object. For
    steady-state sinusoidal fields, the SAR is directly proportional to
    the tissue conductivity, the square of the electric field, and
    inversely proportional to the mass density. The relationship is more
    complex in pulsed or modulated fields, if the intrinsic properties of
    the medium are non-linear. However, since the SAR is related to the
    intensity of the internal electric field, this concept can be used
    independently of the nature of the interaction mechanism responsible
    for biological effects. This stems from the fact that it is the
    internal electric field intensity that quantitatively describes the
    interaction. Nevertheless, it may not be the only factor, e.g.,
    frequency and/or modulation of the radiation field may strongly affect
    biological effects. Consequently, the nature of the radiation fields
    should always be considered in addition to the SAR.

        The SAR is a measure of the absorbed energy which may or may not
    all be dissipated as heat. The temperature is a function of the SAR,
    but it is also a function of the thermal characteristics of the
    absorber (i.e., the size, shape, thermal conductivity).

        The values of the SAR averaged over the whole body and the
    distribution of the SAR have been estimated theoretically and measured
    experimentally in models and experimental animals for various exposure
    conditions. For human subjects, the average SAR for exposures in the
    far field may reach a peak in the frequency range of 30-200 MHz,
    depending on various factors associated with the specific exposure
    situation (Johnson et al., 1976; Durney et al., 1978, 1980). Fig. 11
    presents the average SAR in man and experimental animal models at an
    incident power density of 1 mW/cm2 in free space (far-field)
    conditions. The graphs in Fig. 11 (page 46) show the importance of
    size, frequency, and orientation, while Fig. 12 shows values of
    average SAR at the resonant frequency for several exposure conditions
    for models of man and 2 sizes of rats. This mathematical modelling is
    only possible for greatly simplified models.

        In addition to the average SAR, the SAR distribution in many
    models has been calculated. Much of this work can be found in reports
    by Shapiro et al. (1971), Lin (1976), Gandhi et al. (1979), Kritikos &
    Schwan (1979), and is summarized in the latest edition of the
    Dosimetry Handbook (Durney et al., 1980).

    FIGURE 11

    FIGURE 12

        In the absence of adequate knowledge concerning the mechanisms of
    interactions between microwave energy and biological systems, and in
    the light of the limitations inherent in the SAR, the following
    conclusions can be drawn:

        (a) SAR alone cannot be used for the extrapolation of effects from
    one biological system to another, or for the extrapolation of
    biological effects from one frequency to another.

        (b) Curves for exposure which produce equivalent SAR for a given
    body over the microwave/RF energy spectrum may be used to predict
    equivalent average heating, provided data concerning heat dissipation
    indicates equivalent heat dissipation dynamics. Such curves cannot,
    however, be used as the only basis for predicting biological effects
    or health risks over the microwave/RF spectrum, since from current
    knowledge, it is not possible to state that equivalent average energy
    absorption rate for given radiation frequencies is associated with
    equivalent biological effects.

    6.4  Molecular Absorption

        Despite the photon energies, some recent theoretical explanations
    of experimental observations strongly indicate the possibility of
    interactions at the molecular level. Proton tunnelling, changes in the
    conformation of molecules, and cooperative mechanisms have been
    envisaged (Frhlich, 1968; Illinger, 1971, 1974; Cleary, 1973, 1978;
    Rabinowitz, 1973; Grodsky, 1975; Keilmann, 1977).

        It has been postulated (Frhlich, 1968; Rabinowitz, 1973) that
    microwaves in the frequency region of 60-120 GHz may influence
    macromolecules in biological systems, altering such functions as cell
    division, and virus inactivation or activation. Effects on enzyme
    systems, DNA-protein structures (chromosomes), and cell membranes are
    possible (Grundler & Keilmann, 1978; Pilla, 1979; USSR Academy of
    Sciences, 1973). Physical experimental techniques need developing and
    further studies on biological effects are necessary. Similar
    mechanisms may be operative at lower frequency ranges (Kaczmarek &
    Adey, 1974; Adey, 1975; Grodsky, 1975; Bawin & Adey, 1976) and the
    present status of knowledge about the molecular absorption of
    microwaves and RF in biological systems has been summarized by Straub
    (1978) who states:

            "Absorption of non-ionizing electromagnetic (EM) radiation by
        biologically important molecules can occur by many different
        mechanisms over the frequency range from several hertz through the
        millimeter microwave region. The absorption of EM radiation is
        determined by the bulk dielectric properties of living tissues,
        cells and biomolecules in solution. However, the existence of
        diverse and complex molecular structures characteristic of
        biological systems makes it necessary to consider the details of

        absorption and dissipation of EM energy. In addition, the
        biological function of the molecular species absorbing energy
        needs to be studied to understand the significance of the EM
        absorption. Among many possible examples the following five are
        given: (1) The network of membranous lipid-containing structures
        within and at the outside limit of cells poses a series of
        barriers to thermalization of the absorbed radiation. Thus,
        adiabatic conditions may be maintained in small membrane bound
        volumes for much longer periods of time than in simple solution.
        Large thermal gradients and temperature elevations can result. (2)
        Subsequent temperature elevation may cause membrane structures or
        complex protein assemblies to pass through phase transitions,
        altering their properties. (3) Spatial anisotrophy in the
        arrangement of large molecular assemblies, as found in
        mitochondria and ribosomes, results in specialised functions which
        can he completely changed if some of the molecules are rotated or
        translated by EM radiation. (4) Quantum effects such as proton
        tunnelling with resulting isomerization of DNA base pairs may also
        be influenced by EM radiation. (5) Otherwise random motion of
        "gates" in excitable channels of nerve membranes may be brought
        into forced oscillation by EM radiation, with resultant membrane
        depolarization. Detailed knowledge of structure and function of
        the biological system thus reveals many perturbations which might
        be induced by EM absorption, and, conversely, EM radiation can be
        used to probe biological structures and function."

    7.  BIOLOGICAL EFFECTS IN EXPERIMENTAL ANIMALS

        During the past thirty years, research has been devoted to various
    aspects of the interactions between microwave and radiofrequency
    radiation and biological materials. Unfortunately, most experiments
    have tended to report biological effects as phenomena rather than
    attempting to establish whether such radiation presents a health risk
    to man and other biota. In Czechoslovakia, Poland, and the USSR, a
    continuous research effort made over the last 25-30 years has resulted
    in numerous research reports and reviews (Presman, 1968; Marha et al.,
    1971; Baranski & Czerski, 1976). In the past 20-25 years, interest in
    this field of studies has increased in the USA, first with the
    establishment of the Tri-service Programme in 1956 and then other
    programmes in later years.

        It is impossible to review the numerous studies (see
    bibliographies by Glazer et al., 1976; Glazer & Brown, 1976; Glazer et
    al., 1977) related to the biological effects of microwave radiation
    and only those most pertinent to the evaluation of potential
    biological hazards have been cited. Potentially beneficial effects of
    microwave radiation are outside the scope of this document.

        Only limited information is available from studies of human
    subjects directly exposed occupationally or experimentally to
    microwave radiation. Most of the data on possible harmful effects are
    based on studies of separate cells, simple organisms, animals, and
    models, making it difficult to extrapolate such experimental results
    to man.

        Radiant energy absorption in the living system followed by direct
    interaction with biophysical or biochemical processes, may be defined
    as the primary interaction. Changes in the structure and function of a
    biological system as a result of the primary interaction are
    considered to be biological effects. Immediate biological effects
    arising at the site of the primary interaction may induce further
    indirect changes, both acute and chronic.

        The analysis of data on effects requires the consideration of a
    sequence of events: the physical interaction followed by physiological
    reactions -- local and generalized, and immediate and delayed
    biological effects. In addition, frequent activation of adaptive
    mechanisms may lead to their exhaustion via the classical sequence of
    events of stress-adaptation-fatigue. Consequently, the effects of
    single and repeated exposures should be considered separately, even
    when exposures take place under identical conditions.

        For many years, the primary interaction of microwave and RF
    radiation with living systems was considered almost exclusively in
    terms of electromagnetic field theory (Schwan, 1976, 1978). It was
    concluded that the conversion of the absorbed energy into kinetic

    energy of molecules (i.e., heat) was the only significant mechanism
    involved. However, there are discrepancies between some empirical
    observations and the theoretical explanations available (Cleary, 1973;
    Baranski & Czerski, 1976; Dodge & Glaser, 1977), which indicate that
    "non-thermal" effects may play some role. Direct interference with
    bioelectric phenomena (as seen on the electroencephalogram and the
    electromyogram) and the role of electromagnetic fields in the
    transmission of biological information was suggested by Presman
    (1968), but these hypotheses need experimental verification.

        Interaction of microwave energy at the molecular level has been
    postulated to explain the primary interaction between microwaves and
    parts of living systems such as membranes (Frhlich, 1968; Adey, 1975;
    Bawin et al., 1975; Grodsky, 1975; Bawin & Adey, 1976; Grundler &
    Keilman, 1978; Pilla, 1979).

    7.1  Hyperthermia and Gross Thermal Effects

        Numerous biological and pathophysiological effects have been
    attributed to temperature increases in the tissue resulting from
    absorption of microwave energy. Thermal effects leading to gross
    injury or death have been studied in a number of experimental animals
    and are described here. More subtle effects of thermal origin, caused
    by absorption of microwave energy will be described in later sections.

        The absorption of microwave energy often results in an increase in
    temperature. If the rate of increase exceeds the ability of the
    thermoregulatory system of the organism to dissipate heat,
    hyperthermia will occur, followed by injuries such as burns,
    haemorrhage, tissue necrosis (Cleary, 1978), and death. The extent of
    the damage depends on the thermal sensitivity of the tissue. With
    partial body exposure, highly vascularized tissues show greater
    resistance to thermal damage, because of the more efficient heat
    dissipation. Microwave-induced death in an experimental animal depends
    not only on the quantity of absorbed energy but also on the rate of
    absorption, the animals thermoregulatory system, its physiological
    status, and the environment. Quite different responses to microwave
    exposure have been observed in various species. Table 10 gives the
    survival times of various experimental animals following prolonged
    continuous exposure to microwaves at different frequencies.

        Dogs exposed to microwaves at frequencies of 2.86 GHz, 1.28 GHz,
    and 200 MHz (Michaelson, 1971, 1973) and a power density of
    165 mW/cm2 experienced three distinct phases of hyperthermia. First,
    the body temperature increased by 1-1.4C after about 30 min (the
    extent of the delay depending on the exposure frequency). Second, at
    thermal equilibrium which lasted about 1 h (longer at lower
    frequencies), the rectal temperature stabilized at between 40.5C and
    41C. Finally, the thermoregulatory system could not dissipate the
    heat rapidly enough, the rectal temperature quickly rose above 41C,
    and the animal succumbed. Similar thermal responses have been

        Table 10.  Power densities and exposure times until thermal death in a number of animal
               species at various frequenciesa
                                                                                           

                Power    Exposure                    Rectal
    Species    density     time       Frequency    temperature       Reference
               mW/cm2       min          MHz        increase
                                                       C
                                                                                           

    dog          350          15           200          5            Addington et al. (1958)
                 330          15           200          4            Michaelson (1971)
                 220          21           200          4            Addington et el. (1958)
                 165         270        22 800        4-6            Ely & Goldman (1956)

    rabbit       300          25         2 800        6-7.5          Ely & Goldman (1956)
                 165          40         2 800        > 4            Michaelson (1971)
                 165          30           200        6-7            Ely et al. (1954)
                 100         103         3 000        4-5            Gordon (1966)

    rat          400       13-14        10 000          7            Gordon (1966)
                 300          15         3 000        8-10           Gordon (1966)
                 300          15        24 000          5            Ely & Goldman (1956)
                 150          15         2 400         -             Michaelson (1971)
                 100          25         3 000        6-7            Gordon (1966)
                 100       5-120        mm--dm         -             Gordon (1966)
                  80          35         2 400         -             Michaelson (1971)
                  80          56        24 000         -             Deichmann (1966)
                  50          80        24 000         -             Deichmann (1966)
                  40          90         3 000          7            Gordon (1966)
                  40      30-180        mm--dm                       Gordon (1966)
                  30         135        24 000         -             Deichmann (1966)
                  10         > 5 h      mm--dm         -             Gordon (1966)

    mouse        180           3        24 000                       Deichmann (1966)
                 150           5        24 000                       Michaelson (1971)
                  80          13        24 000                       Deichmann (1966)
                  80          13        24 000                       Michaelson (1971)
                  50          35        24 000                       Deichmann (1966)
                  50          35        24 000                       Michaelson (1971)
                  30         140        24 000                       Deichmann (1966)
                                                                                           

    a  "Adapted from: Baranski & Czerski (1976).
    
    described for dogs with body weights between 4 and 20 kg. No period of
    thermal equilibrium was observed in rats and rabbits exposed at the
    same power density (165 mW/cm2) (Michaelson, 1973).

        Table 11 gives the survival time of rats exposed intermittently to
    24 000 MHz microwaves at 300 mW/cm2. These data provide information
    on a situation corresponding to exposure to a rotating antenna. This
    type of intermittent exposure prolongs the survival time of the
    irradiated animals.

    Table 11.  Survival time of rats following intermittent exposure
               to 24 000 MHz microwaves at 300 mW/cm2 depending on
               the relationship between duration of exposure period 
               and duration of exposures on-offa
                                                                     

          Operation period of         Survival time equal to effective
            the transmitter                   irradiation time
                  (s)                               (min)
              on       off
                                                                     

              60        60                           16.5
               5        15                           28
               3         3                           40
              30        60                           39
              10        20                           65
               3         6                           95
              60       180                           28
              10        30                           76
               3         9                        110 to 120
              30       120                         70 to 75
              15        60                         Over 100
                                                                     

    a  From: Baranski & Czerski (1976) based on Deichmann et al.
      (1959).


        Table 12 provides a summary of data (Baranski & Czerski, 1976) on
    the mass, body surface, and basal metabolic rate of commonly used
    experimental animals. These data can be used to compare the
    experimental results of a microwave-induced thermal load with the
    animal's ability to dissipate heat (its thermoregulatory system).

        Table 12.  Mass, body surface and metabolic rate in various experimental animalsa
                                                                                               

                           Man       Dog       Rabbit    Monkey    Guineapig   Rat      Mouse
                                                                                               

    Mass (kg)              65        15.0       3.5       3.2       0.8         0.2      0.02
    Body surface (m2)       1.83      0.85      0.2       0.26      0.071       0.081    0.085
    Basal metabolic
    rate (W/m2)            45.5      46.0      40.5      30.5      33.7        45.2     26.2
                                                                                               

    a  From: Baranski & Czerski (1976).
    

        In the results presented in Table 10, it was generally assumed
    that the area of the species exposed was approximately one third of
    the body surface, the incident energy was totally absorbed, the heat
    dissipation index was 12 W/m2/C, and that the initial temperature
    difference between body surface and surrounding air was 10C.

        Environmental conditions can influence the thermal response
    (Baranski et al., 1963; Michaelson, 1971). At an ambient temperature
    above normal (40.5C), the animal's thermoregulatory system can
    maintain a normal body temperature, but is not able to cope with an
    additional thermal load produced by microwave exposure. However, at a
    lower ambient temperature (11C), after an initial period of
    adaptation, the microwave radiation does not significantly affect the
    animal's rectal temperature (Michaelson, 1973).

        The influence of environmental conditions on hyperthermia induced
    by microwave radiation exposure can be summarized as follows: (a)
    increasing ambient temperatures and humidity enhance thermal stress;
    and (b) increased air velocity decreases thermal stress.

        In a study by McLees & Finch (1973) in which rats were exposed to
    24 GHz and 300 mW/cm2, it was shown that body cover also affected
    hyperthermia. Animals with and without hair died within 15.5 and 18.5
    minutes, respectively, indicating that clothing could be expected to
    enhance the thermal effects of radiation, unless such clothing
    shielded from, or reflected microwave energy.

        When dogs were anaesthetized using sodium pentobarbital,
    chlorpromazine, or morphine, impaired thermoregulatory responses and
    increased susceptibility to radiation thermal stress were observed
    (McLees & Finch, 1973; Baranski & Czerski, 1976).

        Repeated exposure resulted in physiological adaptation via the
    classical sequence of stress-adaptation-fatigue. Daily exposure of
    dogs to 1280 MHz microwaves for 6 h per day, 5 days per week, for one
    month at a power density of 100 mW/cm2, resulted in an increase in
    rectal temperature with each exposure during the first week. During
    the following 3 weeks, temperature increases were moderate, and a
    progressive reduction in the pre-exposure temperature was observed as
    the number of exposures increased (Michaelson, 1973). These results
    have been confirmed for other species (Gordon, 1966; Phillips et al.,
    1973).

        The blood circulation was considered to be an effective system for
    distribution of the heat generated throughout the body (Michaelson,
    1971), and until recently, the thermal effects of microwaves in
    animals were mainly considered in terms of "volume heating". Guy and
    his associates (Guy, 1971, 1974; Johnson & Guy, 1972) using phantom
    models, developed elegant thermographic techniques and demonstrated
    convincingly very nonuniform deposition of microwave energy, expected
    to result in nonuniform deep body heating. In physiological terms,
    this means that absorbed energy may cause local thermal stimulation or
    gross effects on different organs depending on the exposure level.

    7.2  Effects on the Eye

        Studies on the effects of microwave radiation on the eye were
    carried out as early as 1948 (Richardson et al., 1978). Most animal
    studies have been conducted on the New Zealand white rabbit because
    its eye is similar to the human eye.

        Investigations to determine cataractogenic radiation levels and
    lengths of exposure at various frequencies have been conducted in both
    the far and near fields. In far-field studies, the whole of the body
    of the animal is exposed but, in some cases, this results in the
    animal's death. Near-field techniques involve exposing the eye at some
    distance from the source and permitting air to circulate against the
    eye, or exposing the eye by direct contact with a source of microwave
    energy, so that there is no air circulation. The conditions of
    exposure have a considerable influence not only on the development of
    cataracts but also on their location in the eye. When air circulation
    is permitted, the exposure causes opacities to develop in the
    posterior subcapsular cortex of the lens. Without an air gap,
    opacities develop in the anterior subcapsular cortex (Carpenter et
    al., 1974b).

        Guy and his colleagues (1975b) have recently determined threshold
    power density levels and durations of exposure for cataract formation
    in rabbit eyes with a single exposure to 2.45 GHz near-field
    radiation. Their results are in good agreement with earlier data
    obtained by Carpenter and his co-workers (1974b) as shown in Fig. 13.
    At 2.45 GHz, the maximum temperatures occurred near the posterior

    FIGURE 13

    surface of the lens, and irreversible changes in the lens took place
    in the posterior cortical area only. Other changes in the exposed eye
    were found to be transient in nature and disappeared within two days
    of irradiation. The minimum power density level at which cataracts
    were formed appeared to be 150 mW/cm2 for 100 min corresponding to a
    maximum specific absorption rate in the vitreous body of 138 W/kg. The
    threshold temperature in the eye for cataract formation was estimated
    to be about 41C (Guy et al., 1975b).

        To investigate the mechanism by which microwaves produce cataracts
    at 2.45 GHz, rabbits were subjected to general hyperthermia and local
    heating of the lens (Kramer et al., 1976). Rabbits, under general
    hyperthermia, were kept at a temperature above 43C for 35 minutes.
    After 4-6 months, the only cataracts observed occurred in eyes damaged
    by insertion of the temperature probes. The authors concluded that
    basic differences occur when heating by means of microwave energy and
    by convective hyperthermia. Eyes irradiated with microwaves show a
    characteristic temperature gradient, with the highest temperature
    behind the lens, whereas in hot bath experiments, the highest
    temperature occurs at the surface of the cornea. Further high-level
    microwave exposure raises the eye temperature within minutes, compared
    with at least 2 h in the hot water bath. Thus, a sharp temperature
    gradient and a high rate of heating rather than gradual, more uniform
    heating may be necessary to produce cataracts (Kramer et al., 1976).

        In studies to investigate the relative cataractogenic effects of
    exposure to two frequencies, 2.45 and 10 GHz, a special dielectric
    lens was used to irradiate the eyes of New Zealand white rabbits,
    selectively. With a constant power density, exposure to 10 GHz induced
    a higher intraocular temperature than exposure to 2.45 GHz. However,
    when the animals were exposed to these frequencies for the same length
    of time, cataracts were induced at lower power densities at 2.45 GHz
    than at 10 GHz (Table 13). Although opacities formed in the posterior
    subcapsular cortex of the lens at both frequencies, their initial
    appearance and subsequent development differed. Radiation at 2.45 GHz
    induced posterior cortical banding within 1 or 2 days, followed by the
    appearance of small granules along or on the horizontal line of the
    posterior suture. Occasionally small vesicles developed. Some
    opacities also had a fibrillar, cotton-like appearance, and
    superficial damage, such as pupillary constriction and hyperaemia of
    the bulbar and palpebral conjunctiva was observed within 24 hours
    (Hagan & Carpenter, 1976).

        In one of the very few investigations of chronic, low-level
    exposure of rabbits' eyes (2 mW/cm2 for 8 h per day, 5 days a week,
    for 8-17 weeks at 2.45 GHz), ocular changes were not observed up to 3
    months after termination of exposure (Ferri & Hagan, 1976).

        Table 13.  Production of cataracts in the eyes of rabbits by a single 30-min exposure
               to 2.45 GHz or 10 GHz
                                                                                             

                                   2.45 GHz                           10 GHz
      Incident power      Number of      Development of       Number of       Development of
     density (mW/cm2)    experiments   lens opacities (%)    experiments    lens opacities (%)
                                                                                             

            275              12                 8                --                --
            295              12                67                --                --
            310              12                58                12                 0
            325              12               100                --                --
            345               2               100                12                50
            375              --                --                12                67
            410              --                --                11                82
            440              --                --                 2               100
                                                                                             

    a  From: Hagan & Carpenter (1976).
    

        When the cataractogenic power density levels for continuous wave
    and pulsed radiation were compared at a few frequencies, no
    differences in the threshold levels for cataractogenesis were found
    (Carpenter & Van Ummersen (1968); Carpenter (1969); Birenbaum et al.
    (1969); Williams & Finch (1974); Weiter et al. (1975). The average
    power density, not the peak power density, appears to be the critical
    field parameter in cataract induction.

        Most authors including Belova (1960), Carpenter et al. (1974b),
    Paulson (1976), Kramer et al. (1978) and Steward-Dehaan et al. (1979)
    have tended to relate microwave cataracts to the secondary effects of
    local temperature increase. The conventional view is that, as the
    crystalline lens does not have its own blood supply, it is easily
    overheated with consequent damage to capsular cells and denaturation
    of the protein in the lens.

        Studies have been performed to determine if cataracts can be
    formed by an accumulation of exposures at subthreshold levels. In one
    experiment, rabbits' eyes were exposed for 3 min to 2.45 GHz radiation
    at a power density of 280 mW/cm2 (5 min exposure was required to
    induce a cataract after a single exposure). When the 3-min exposure
    was given once a day for 5 days, the animals developed cataracts.
    However, if the eyes were exposed under the same conditions, but with
    a break of 7 days between exposures, cataracts did not develop

    (Carpenter, 1969). In an earlier study, rabbits' eyes were exposed to
    2.45 GHz at a power density of 80 mW/cm2 for 60 min daily, for 10 or
    15 days (Carpenter & Van Ummersen, 1968). Cataracts appeared 1-6 days
    after treatment. However, the authors later indicated that the power
    density measurement was inaccurate and that subsequent measurements
    showed that the actual power density was greater than 80 mW/cm2.

        Paulsson et al. (1979) studied the eyes of rabbits exposed to
    3.1 GHz pulsed (pulse length 1.4 s, repetition frequency 300 Hz)
    radiation at an average intensity of 55 mW/cm2 (1.3 MW/m2 peak)
    either to single exposures of 1-1 h or, after a series of repeated
    1-h exposures, for up to 53 h during 100 days. Degenerative changes in
    the retinal neurons and synaptic boutons, and reactive changes in
    glial cells were observed only following the repeated exposures. No
    evidence was found of increased permeability of the blood-retina
    barrier.

        Effects of millimetre waves (35 and 107 GHz) at power densities
    ranging from 5 to 60 mW/cm2 for 15 min-1 h were investigated in
    rabbit eyes by Rosenthal et al. (1976). Corneal damage and epithelial
    and stromal injury were observed. Stromal injury appeared at lower
    power densities (5 mW/cm2) at a frequency of 107 GHz than at 35 GHz,
    but it was concluded that keratitis (inflammation of the cornea) was a
    useful criterion for ocular response to millimetre radiation.
    Keratitis occurred at lower power densities than those required to
    produce other ocular effects such as iritis or lenticular injury. The
    recovery rate from stromal injury depended on the frequency of the
    radiation and was faster after exposure to 107 GHz.

        The following conclusions on the effects of microwave radiation on
    the eye can be drawn from these and other data from literature
    reviews:

        (a) Above 500 MHz, opacities of the eye may be produced when power
    densities exceed 150 mW/cm2, if the duration of exposure is
    sufficiently long;

        (b) Although ocular injury has not been reported at frequencies
    below 500 MHz, its possibility cannot be excluded;

        (c) The frequency of the microwave radiation influences the type
    and location of the injury to the eye;

        (d) Exposure conditions, namely whether in the near field or far
    field, whole body or selective exposure of the eye, eye exposure with
    or without an air gap (to provide cooling), and the temperature of the
    animal's body, all influence the power density and duration of
    exposure needed to produce eye injury.

        (e) Injury to the eye from microwaves appears to be predominantly
    thermal in nature, temperature gradients within the eye and the rate
    of heating being two major factors in the stress that leads to injury.
    Non-thermal effects cannot be excluded but they alone do not appear to
    be sufficient to produce effects in the eye, although they may provide
    a necessary mechanism of interaction.

        (f) As can be seen in Fig. 13 (p. 55) the threshold curve of power
    densities versus time to produce eye cataracts is not linear. Exposure
    of the eye at each frequency seems to require a threshold microwave
    power density below which even continuous exposure does not produce
    eye injury. This would appear to exclude the possibility of
    cataractogenesis caused by low level chronic exposure, and this was
    confirmed in a recent experiment (Ferri & Hagan, 1976).

        (g) Pulsed and continuous wave radiation with the same average
    power density level seem to possess the same potential for cataract
    induction. However, effects from pulsed radiation with a small duty
    factor and high peak power cannot yet be excluded;

        (h) Cataracts can be produced by repeated exposures to
    sub-threshold power density levels. For this cumulative effect to
    occur, the levels have to be sufficiently high that a slight but
    persistent injury is not fully repaired before another exposure takes
    place. However, if the time between exposures is sufficiently long for
    repair to take place, cumulative damage is not observed.

    7.3  Neuroendocrine Effects

        Interaction between the endocrine and nervous systems is very
    important to the functioning of the human body. The hypothalamus
    within the brain is a control centre involved in the regulation of the
    autonomic nervous system, including such visceral functions as
    temperature control within the whole body. This gland, coordinated by
    the central nervous system (CNS), releases specific factors into the
    pituitary portal system, which regulate hormones released by the
    endocrine organs. The endocrine system can be considered as a feedback
    control system where the hypothalamus, via the pituitary, causes
    hormones to be secreted by endocrine glands. Once the endocrine
    hormones have reached a certain level, this information is fed back to
    the pituitary and hypothalamus, causing a reduction or cessation in
    hormone secretion. The system's actions are modified by direct neural
    inputs from higher brain centres and peripheral nerves.

        Descriptions of the biochemical and neuroendocrine aspects of
    exposure to microwaves can be found in recent reviews by Michaelson et
    al. (1975) and Cleary (1977).

        Dogs exposed to 3 GHz microwaves at 10 mW/cm2 showed a
    substantial increase (100%-150%) in corticosteroid levels, a decrease
    in blood potassium, and an increase in blood sodium content (Petrov &
    Syngajevskaja, 1970). The increase in the corticosteroid levels during
    and after irradiation may have been an adaptive reaction, since in
    some animals the adrenocortical function becomes inhibited and
    sensitivity to microwave radiation increases because of insufficient
    release of adrenocorticotropic hormone (ACTH).

        Dumanskij & Sandala (1974) found that chronic low-level exposure
    of rats and rabbits to 3 cm, 12 cm, and 6 m microwaves at 10 W/cm2
    and below, for 8-12 h per day, for 120 days, reduced cholinesterase
    and increased 17-ketosteroid levels in the urine during the 60 days
    following irradiation. A reduced amount of ascorbic acid in the
    adrenal glands and reduced adrenal gland weight were also observed.
    Syngajevskaja et al. (1962) exposed dogs and rabbits (162 animals) to
    decimeter waves at 70 mW/cm2 for 30 min and reported increases in
    the ascorbic acid concentration in the adrenals, while exposure at
    5 mW/cm2 for 30 min caused it to decrease. Changes in glucose levels
    in the blood and variations in liver glycogen content were observed;
    lactic acid levels were also affected. It has been suggested that a
    whole body rise in temperature caused by microwave exposure suppresses
    the hormone-producing functions of the anterior pituitary and
    adrenals, while exposures not resulting in an increased rectal
    temperature enhance hormone production (Petrov & Syngajevskaja, 1970).

        No significant alterations were observed in growth hormone or
    thyroxine levels in barbiturate-anaesthetized dogs, cranially exposed
    to 2.45 GHz microwaves at various power densities (20-80 mW/cm2) for
    1 h (Michaelson et al., 1975). When rats were exposed (whole body) for
    1 h to 2.45 GHz microwaves at 9 mW/cm2 an increase in growth
    hormones was observed, but at 36 mW/cm2 exposure, a significant
    decrease was noted (Syngajevskaja et al., 1962).

        The thyroid activity in rats exposed to 2.45 GHz microwaves at
    1 mW/cm2 for 8 h per day for 8 weeks was studied by Milroy &
    Michaelson (1972). No structural or functional changes were detected,
    other than those that could be attributed to microwave-induced thermal
    stress. In contrast, Baranski et al. (1973) reported that rabbits
    exposed to 10 cm microwaves at 5 mW/cm2 showed increased thyroid
    activity. Mikolajczyk (1977) suggested that these differences in
    results were due to the experimental procedure and conditions rather
    than the differences in species.

        When rats were exposed to 2.45 GHz microwaves at 10, 15, 20, and
    25 mW/cm2 for 4, 16, and 60 h (i.e., 64 h with two 2-h breaks),
    Parker (1973) found that the iodine-concentrating ability of the
    thyroid serum, protein-bound iodine levels, and thyroxine increased
    slightly at 10 mW/cm2, but decreased at 20 and 25 mW/cm2 during

    the 16-h exposure. Exposure at 15 mW/cm2 for 60 h resulted in a
    decrease in protein-bound iodine and thyroxine, and a decrease in the
    ability to concentrate iodine.

        When male rats were exposed to 2.87 GHz radiation at 10 mW/cm2
    for 6 h per day, 6 days per week for 6 weeks, there were no
    significant differences between the average body and organ weights of
    irradiated and control animals (Mikolajczyk, 1977). Although the
    levels of growth hormone in the anterior pituitary were the same in
    both groups of rats, a significantly higher level of luteinizing
    hormone (LH) was found in the irradiated animals. It was suggested
    that changes in the LH activity might be due to the influence of
    microwave exposure on the pituitary, or on hypothalamic function or on
    both.

        Various animal studies in which neuroendocrine effects have been
    reported following exposure to low intensity fields are summarized in
    Table 14. Baranski & Czerski (1976) state in their review of endocrine
    effects that it is extremely difficult to sum up the evidence. All
    aspects of microwave interactions reported need further investigation
    concerning both the cause and dose dependence of the effects described
    and the mechanisms involved. However, it could be stated that:

        (a) Microwave radiation induces endocrinological changes that may
    be due to stimulation of the hypothalamic-hypophyseal system, through
    thermal interaction at the hypothalamus, or immediately adjacent
    levels of organization, the pituitary, the particular endocrine gland,
    or the end-organ.

        (b) Since the neuroendocrine system is homeostatic, transient
    neuroendocrinological changes should not be equated with pathological
    alterations.

        (c) Sufficient data are available to indicate that the response of
    the neuroendocrine system to microwaves depends on the frequency,
    power density, the duration of exposure, and the part of the body
    exposed.

        (d) The nonuniform distribution of microwave energy within the
    body seems to be an important factor affecting the response of the
    neuroendocrine system.

        (e) Several components of the neuroendocrine system are critically
    sensitive to environmental temperature, thus low-power density,
    microwave-induced effects could result from sensitivity to small
    changes in temperature.

        (f) From available data, it would seem that direct interaction of
    microwaves with components of the neuroendocrine system cannot be
    excluded.


        Table 14.  Neuroendocrine effects of exposure to low intensity fieldsa
                                                                                                                 

    Independent             Dependent         Experimental      Results and comments          Reference
    variables               variables         subject
                                                                                                                 

    10 cm, cw;              endocrine         rats              Increase in gonadotropic      Mikolajczyk (1972)
    0.01, 1, 3,             gland hormone     (in vivo)         tropic hormones
    10, 20 & 150            levels                              followed by decrease
    mW/cm2; 1 h/day,                                            18 h after exposure at
    single or repeated                                          10 Mw/cm2 or greater
    exposures                                                   intensities; alteration
                                                                in hypothalamic function
                                                                governing the follicle-
                                                                stimulating hormone (FSH)
                                                                and luteinizing hormone
                                                                (LH) release from
                                                                pituitary; no changes
                                                                in corticosteroid content
                                                                of adrenals or
                                                                blood at 10 mW/cm2
                                                                for 15, 30, or 60 min.

    10 cm, cw;              adrenal           rats              Initial decrease in           Leites &
    100 mW/cm2              alterations       (in vivo)         Sudan III stain-positive      Skuricina (1961)
    10 min exposure/                                            lipids, birefringent
    day for 14 days                                             substances, &
                                                                ascorbic acid; Increase
                                                                in all variables
                                                                during course of exposure
                                                                return to normal 2 weeks
                                                                after exposure.
                                                                                                                 

    Table 14 (Cont'd)
                                                                                                                 

    Independent             Dependent         Experimental      Results and comments          Reference
    variables               variables         subject
                                                                                                                 

    decimetre waves,        adrenal cortex    rats              No effect on serum            Nikogosjan (1962)
    40 mW/cm2; 1-h          alterations,      (in vivo)         Na+ or K+; Increase
    daily exposure,         serum                               In Ca+2 and C--1 In
    prolonged               electrolytes                        serum and urine.
    duration.

    15 mW/cm2; 60 h         neuroendocrine    rats              Transient changes             Michaelson et al.
    up to 60 mW/cm2;        responses         (in vivo)         in plasma corticosterone,     (1977) and Lotz &
    up to 2 h                                                   growth hormone, and           Michaelson (1978)
                                                                thyroid hormone levels
                                                                (20-30 mW/cm3 seemed
                                                                to be the transitional
                                                                range for stimulation
                                                                of pituitary --
                                                                adrenal activation);
                                                                noted effects correlated
                                                                with temperature
                                                                increases in endocrine
                                                                gland.

    2.45 GHz, cw;           thyroid           rats              No structural or              Milroy &
    1 mW/cm2;               function          (in vivo)         functional changes            Michaelson (1972)
    continuous exposure,                                        other than those
    8 wk; 10 mW/cm2,                                            attributable to
    8 h/day for 8 wk                                            thermal stress.
                                                                                                                 

    Table 14 (Cont'd)
                                                                                                                 

    Independent             Dependent         Experimental      Results and comments          Reference
    variables               variables         subject
                                                                                                                 

    2.45 GHz, cw;           thyroid           rats              23% decrease in               Parker (1973)
    15 mW/cm2 60 h          function          (in vivo)         protein-bound iodine
    exposure                                                    and 55% decrease
                                                                in serum thyroxine.

    2.86-2.88               survival          rats time,        Survival time of              Mikolajczyk (1974)
    GHz, cw;                endocrine         (in vivo)         hypophysectomized
    10-120 mW/cm2           function                            rats increased at
                                                                120 mW/cm2; 2-week
                                                                habituation before 
                                                                exposure alterations in
                                                                corticosterone
                                                                levels; daily exposures
                                                                at 10 mW/cm2 for 1
                                                                month did not alter
                                                                gonadotropins (LH
                                                                and FSH) but single
                                                                exposures induced
                                                                detectable alterations.

    10 cm, cw;              carbohydrate      rabbits           Changes in serum              Baranski et al.
    5 mW/cm2 (free          metabolism,       (in vivo)         pyruvic and lactic            (1967)
    field exposure)         skeletal                            acid; decrease in
                            muscle                              skeletal muscle 
                            metabolism                          glycogen; altered 
                                                                electromyography indicative
                                                                of changes in
                                                                muscle metabolism;
                                                                altered carbohydrate
                                                                metabolism.
                                                                                                                 

    Table 14 (Cont'd)
                                                                                                                 

    Independent             Dependent         Experimental      Results and comments          Reference
    variables               variables         subject
                                                                                                                 

    10 cm, cw;              thyroid           rabbits           Increased radioiodine         Baranski et al.
    5 mW/cm2                function          (in vivo)         uptake, histological          (1973)
    repeated exposure                                           & electronmicroscopic
                                                                signs of thyroid 
                                                                hyperfunction.

    10 cm, cw;              adrenal           rabbits           Decrease 17-hydroxy-          Lenko et al. (1966)
    50-60 mW/cm2,           function          (in vivo)         corticosteroid in
    4 h/day                                                     urine, first 20 exposures;
                                                                return to normal
                                                                at day 10 due
                                                                to adaptation; no
                                                                changes in 17-hydro-
                                                                xycorticosteroid in
                                                                urine.

    metre & decimetre       endocrine         dogs, rabbits     Increased adrenal             Syngajevskaja
    waves; 70 mW/           function          (in vivo)         ascorbic acid                 et al. (1962)
    cm2; 30 min                                                 concentration following 70
                                                                mW/cm2, decrease following
                                                                5 mW/cm2, thermal 
                                                                intensities suppress 
                                                                pituitary & adrenal 
                                                                functions; low-intensity 
                                                                exposure stimulates.
                                                                                                                 

    Table 14 (Cont'd)
                                                                                                                 

    Independent             Dependent         Experimental      Results and comments          Reference
    variables               variables         subject
                                                                                                                 

    1.24 GHz, pw;           thyroid           dogs              Increased radioiodine         Howland &
    360 Hz pulse            alterations       (in vivo)         uptake 4-25 days              Michaelson (1959)
    repetition rate;                                            after exposure: radio-
    2 ms pulse, 50                                              iodine uptake 
    mW/cm2; average                                             increased 3-4 years
    power; 6 h/day                                              after single 100 mW/
    for 6 days                                                  cm2 exposure to 1.28
                                                                GHz, pw.

    2.45 GHz, cw;           neuroendocrine    dogs              Transient increased           Michaelson et al.
    20-40 mW/cm2;           responses         (in vivo)         mean plasma                   (1977b)
    2 h                                                         corticosterone levels,
                                                                correlated with mean
                                                                colonic temperature.
                                                                                                                 

    a  Adapted from: Cleary (1978).
    

    7.4  Nervous System and Behavioural Effects

        Microwave radiation effects on the central nervous system and
    behaviour have been the subject of most controversy in the whole field
    of bioeffects. Czechoslovak, Polish, and Soviet investigations on this
    subject commenced in the early fifties and have been the source of
    most of the reports on the effects of microwaves on man. Animal
    studies and clinical and industrial surveys in Czechoslovakia, Poland,
    and the USSR have been summarized by Marha et al. (1971), Baranski &
    Czerski (1976), and Presman (1968), respectively. The basic assertion
    is that exposure to microwaves at low power densities results in
    neurasthenic disorders in man. Subjective complaints such as headache,
    fatigue, weakness, dizziness, moodiness, confusion, and nocturnal
    insomnia have been reported. In small experimental animals, chronic
    and repeated exposures at incident power densities of 10 mW/cm2 or
    less have been reported to lead to disturbances in conditioned
    reflexes and to behavioural changes (Kholodov, 1966; Presman, 1968;
    Petrov et al., 1970; Prey, 1971, 1977; Marha, 1971; Lobonova, 1974;
    Galoway, 1975; Hunt et al., 1975; Serdjuk, 1977; Cleary, 1978).
    Studies of microwave/RF exposure effects on conditioned and normal
    reflexes, as well as on behaviour, were carried out on mice, rats,
    guineapigs, rabbits, dogs, monkeys and in some instances on birds
    (Romero-Sierra et al., 1974; Bigu-del-Blanco et al., 1975; Bliss &
    Heppner, 1977).

        Numerous reports of the sensitivity of the human CNS to low level
    microwave exposure have stimulated interest in the subject with a
    consequent increase in studies on microwave effects on the animal CNS
    (Cleary, 1977). Investigations have been conducted at various levels
    of CNS organization and range from studies of isolated nerves (McRee &
    Wachtel, 1977) to behavioural studies in primates (De Lorge, 1976,
    1979). These studies were established to determine if the effects were
    thermally-induced or were the result of the direct action of
    microwave-energy on the CNS. The results of many studies can be
    explained by the nonuniform distribution of thermal energy and/or
    thermal gradients, but the results of others such as the increase in
    calcium efflux from cerebral tissue, due to specific amplitude
    modulation are difficult to explain on the basis of heating.

        Disturbances in the bioelectric function of the chick forebrain
    with calcium efflux were observed following  in vivo exposure to
    147 MHz radiation, amplitude modulated at 9-20 Hz (Bawin et al.,
    1975). These effects could not be obtained when the frequency of
    amplitude modulation was between 6 and 9 Hz or between 20 and 35 Hz. A
    20% increase in calcium was also observed by Kaczmarek & Adey (1974)
    in the cat brain after  in vivo exposure to 10 ms pulsed radiation at
    200 Hz, 20-50 mV/cm2. Further research is needed since these effects
    may depend on a direct interaction of electromagnetic fields with the
    cellular membrane (Grodsky, 1975; Straub, 1978; Kolmitkin et al.,
    1979).

        Blackman et al. (1979) recently confirmed the work of Bawin and
    Adey and their coworkers, in finding that calcium efflux from brain
    tissue depended on amplitude modulation frequency and power levels.
    Increased calcium efflux appeared at amplitude modulation frequencies
    around 9 Hz, peaked from 11-16 Hz, and disappeared above 20 Hz as
    shown in Fig. 14. It can be said that a "frequency window" exists for
    this phenomenon. Calcium efflux appears at 0.5 mW/g, reaches higher
    values at 0.75 mW/g and decreases at 1.0 mW/g. Thus, it can be said
    that "power windows" also exist. These may shift with frequency
    (Blackman et al., 1979).

    FIGURE 14

        The electrical activity of the brain, measured by means of an EEG,
    may be influenced by a wide variety of exposure regimes. Acute single
    exposures to 40 mW/cm2 or more, induce transient changes in EEG
    patterns. Early experimentation in this area has been summed up by
    Kholodov (1966). Long-term, repeated exposures of dogs, cats, rabbits,
    rats, frogs, and mice at power densities between 2 and 5 mW/cm2 were
    reported to lead to alterations, such as the desynchronization of
    basal rhythms and later a flattening in EEG tracings (Baranski &
    Edelwejn, 1968; Bychkov & Dronov, 1974; Bychkov et al., 1974; Gillard
    et al., 1976). However, these earlier reported effects are
    questionable since experiments were carried out using EEG electrodes
    or wires that significantly perturbed the field.

        Mice, rats, and rabbits subjected to long-term, low or
    medium-level (about 1-5 mW/cm2) exposure were reported to show an
    increased susceptibility to convulsant drugs (Baranski & Edelwejn,
    1968; Servantie et al., 1974, 1975; Krupp, 1977). Detailed analyses of
    EEG data and results of pharmacological studies indicate that the
    reticular formation of the midbrain is the structure in which exposure
    to microwaves and RF may induce effects at low incident power density
    levels.

        The mechanism of changed susceptibility to drugs acting on the
    nervous system, particularly convulsant drugs, after repeated
    microwave exposures is unclear. On the other hand, as the action of
    many drugs is well understood, the phenomenon may serve to clarify
    mechanisms of action of microwave and RF radiation on the nervous
    system (Czerski, 1975). The phenomenon has practical implications in
    the case of the medication of microwave workers.

        Structural changes in the nervous tissue of rabbits and hamsters
    which were demonstrable by electron and light microscopy, were
    reported following single exposures to 2450 MHz microwaves at power
    densities of 25-50 mW/cm2 (Baranski, 1967; Baranski & Edelwejn,
    1979; Albert & De Santis, 1975; Albert, 1979). In their study on
    rabbits subjected to single or repeated exposures to continuous or
    pulsed microwaves (2950 MHz), Baranski & Edelwejn (1974) did not find
    any effects on acetylcholinesterase activity after long-term exposure
    (2 h/day for 3-4 months to 3.5-5 mW/cm2).

        Brain hyperaemia, pyknosis, and vacuolization of nerve cells were
    observed in rats repeatedly exposed for 75 days to 3- and 10-cm
    microwaves at high power densities (40-100 mW/cm2) (Tolgaskaya et
    al., 1962; Tolgaskaya & Gordon, 1973). These effects were less
    pronounced following exposures at 10-20 mW/cm2 and with exposure to
    3-cm microwaves compared with 10-cm microwaves at the same power
    density. The effects were reversible, several days after termination
    of the experiment.

        The blood-brain barrier of rats may be affected by pulsed and
    continuous wave microwave radiation at 1.2 GHz (Frey et al., 1975). A
    single exposure of 30 min at an average power density of 0.2 mW/cm2
    pulsed and 2.4 mW/cm2 continuous wave radiation led to an increase
    in permeability. In another study on rats, Oscar & Hawkins (1977)
    found temporary alterations in permeability following single 20-min
    exposures to 1.3 GHz radiation at power densities of about 1 mW/cm2
    pulsed and 3 mW/cm2 cw. Many other investigators including Merrit
    (1977) and Sutton & Carrell (1979) were unable to reproduce these
    experimental results.

        In studies by Wachtel et al. (1975), exposure of individual
    neurons to 1.5 GHz and 2.45 GHz microwave radiation at a dose rate of
    approximately 10 mW/g had a marked effect on the firing pattern of
    Aplysia neurons. Although heating may have been partially responsible,
    the authors suggest that other factors are needed to explain the
    effect. Rectification of the applied field in nerve tissue could
    explain the observed effects.

        The threshold power density required to evoke potentials in the
    brain stem of cats using nonperturbing electrodes was found to be
    approximately 0.03 mW/cm2 with a peak of 60 mW/cm2 for frequencies
    between 1.2-1.5 GHz (Frey, 1967).

        Stverak et al. (1974) found that rats having an inherent
    predisposition to epileptic seizure after sound stimulation showed
    reduced sensitivity of this phenomenon following long-term (4 h/day
    for 10 weeks) exposure to 2850 MHz radiation, pulsed for 10 s,
    repetition frequency 769.2 Hz, at an average power density of
    30 mW/cm2.

        Behavioural perturbations in rats in the form of work stoppage
    have been reported by Justesen & King (1970) and Lin et al. (1979).
    Exposure of hungry unrestrained rats to 2.45 GHz microwaves at a dose
    rate of approximately 9 mW/g caused stoppage of work for food after
    20 min of exposure in a multimode cavity (Justesen & King, 1970). With
    restrained rats irradiated with near-field radiation at 918 MHz, the
    threshold dose rate for the effect was 8 mW/g (Lin et al., 1979). It
    was calculated by Justesen (1978) that an integral dose between 8 and
    10 J/g was required for work stoppage in hungry rats, e.g., 23 min
    exposure to an average power density of 20 mW/cm2 at 600 MHz
    (resonant frequency for the rat) or 46 min exposure to the same power
    density at 400 MHz. The work stoppage was found to be related to the
    specific absorption rate, suggesting a thermal basis for the effect.

        In studies by Moe et al. (1977), rats exposed for 210 h to 918-MHz
    radiation at 10 mW/cm2 showed decreased locomotor activity and food
    intake. This behavioural change could be attributed to thermal
    loading, even though the animals were not under hyperthermic stress.

        The effects on exploratory activity, swimming, and discrimination
    involving a vigilance task were studied in rats exposed to 2.45 GHz
    pulsed radiation (Hunt et al., 1975). A dose rate of 6 mW/g caused a
    moderate decrease in the level of exploratory activity and swimming
    speed. The results were attributed to fatigue from thermal
    overexposure, since the effect on vigilance discrimination was
    observed to be directly related to induction of and recovery from
    hyperthermia. Nearly lethal radiation (11 mW/g) initially produced a
    marked degradation in performance, but the rats returned to the
    trained level of proficiency after 1 h.

        Microwave radiation was found to affect the behaviour of rats
    conditioned to respond to multiple schedules of reinforcement (Thomas
    et al., 1975). Exposure for 30 min to 2.86- and 9.6-GHz pulsed
    radiation, and to 2.45-GHz cw radiation just before experimental
    sessions at power densities exceeding 5 mW/cm2 caused significant
    alterations in behaviour.

        Roberti et al. (1975) did not find any difference in the
    spontaneous motor activity of rats after exposure for periods
    totalling 408 h to 10.7- and 3-GHz microwaves at power densities
    ranging from 0.5 to 26 mW/cm2. Classical Pavlovian methods were used
    by Svetlova (1962) and Subbota (1972) to investigate reflex and
    conditioned reflex actions in microwave-irradiated dogs, by
    determining the time of initiation of saliva secretion following the
    conditioning stimulus, the latency time, and the number of drops
    secreted. After lateral exposure to 10-cm microwaves for 2 h at power
    densities ranging from 1-5 mW/cm2, the intensity of the response
    increased on the opposite side, and the latency time was shortened.
    However, following 70 h of exposure in 35 days (2 h/day), the
    conditioned responses became identical to those before irradiation
    showing that a gradual adaptation of the dogs' responses to successive
    microwave exposures occurred.

        Galloway (1975) investigated the effects of 2.45 GHz cw microwave
    exposure on discrimination and acquisition tasks in trained rhesus
    monkeys. The heads of the animals were exposed directly with energy
    deposited at rates ranging from 5 to 25 W (for a 1.2 kg head the
    resulting average dose rate was between 4 mW/g and 21 mW/g). Before
    testing, the monkeys were given a dose of 2.5 J/g over 2 min.
    Convulsions occurred in all animals irradiated at 25 W and in some at
    15 W, an integral dose approaching 25 J/g (the dose required to
    produce convulsions (Justesen, 1978)) was given. It is apparent that
    hot spots were produced in the monkey's brains to induce this effect.
    Exposure to 10 W for 5 days, for 40 min per day did not produce any
    performance deficit, even in animals suffering from skin burns and
    severe convulsions caused by exposure to high power radiation.

        The performance of a vigilance task was investigated in rhesus
    monkeys after whole body exposure to 2.45 GHz far-field radiation.
    Behaviour was not disrupted provided that increases in colonic
    temperature did not exceed 1C. With a 1-h exposure, the threshold of
    behavioural disruption was 70 mW/cm2 (De Lorge, 1976).

        Exposure to continuous wave microwave radiation of 1.2 GHz at
    average power densities of 10-20 mW/cm2 did not affect skilled motor
    performance in monkeys even when the animals were positioned for
    maximum energy deposition in the brains and subjected to three 2-h
    periods of exposure (Scholl & Allen, 1979).

        A number of studies including some of those already discussed and
    others for comparison are summarized in Table 15. The results obtained
    by different investigators vary according to exposure conditions and
    the end-point investigated. Interpretation of these observations is
    difficult since many observations are either controversial or
    contradictory. Data tend to be better substantiated at power densities
    above 5-10 mW/cm2.

        In 1961, Frey reported the sensory effect of "microwave hearing".
    Man perceives an audible clicking or buzzing sensation on exposure to
    pulsed radiation at low power densities. He (Frey, 1971) considered
    that the effect was caused by direct neural stimulation but later
    studies by Foster & Finch (1974) and Chou et. al., (1977) have
    strongly indicated that an electromechanical interaction occurs due to
    thermal expansion. The threshold of microwave hearing is approximately
    10 mJ/g per pulse and is independent of the pulse width for pulses of
    less than 30 microseconds (Guy et al., 1975a). Microwave hearing is
    now thought to be caused by a small but fast rise in temperature
    which, by thermal expansion, generates a wave of pressure exciting the
    cochlea.

        To summarize, it can be stated that studies on the effects of
    microwaves/RF radiation on the nervous system indicate that exposure
    at low-power densities appears to induce detectable changes in some
    cases (Cleary, 1977). While there seems to be evidence that, at
    sufficiently high intensities (above 1-5 mW/cm2), nonuniform heating
    of various critical organs takes place in experimental animals, it is
    not possible at present to exclude other mechanisms. Furthermore, it
    is difficult to evaluate the significance of microwave-induced
    behavioural effects because of the general lack of quantitative
    correlations between thermal effects at low power densities and
    responses at the physiological or psychological levels of analysis
    (Cleary, 1977).


        Table 15.  Neural effects of exposure to low-intensity fields
                                                                                                                 

    Independent             Dependent         Experimental
    variables               variables         subject           Results and comments          Reference
                                                                                                                 

    200 Hz; 10 ms           cerebral          cat-direct        20 % increase in              Kaczmarek &
    pulsed field;           Ca+2              cortical          Ca+2 efflux                   Adey, (1974)
    20-50 mV/cm             efflux            stimulation       from neurons.
                                              (in vivo)

    147 MHz. AM             cerebral          chick fore-       Increase in Ca +2             Bawin et al.
    modulated at            Ca+2              brain             from neurons; no              (1975)
    6, 9, 11, 16 Hz;        efflux            (in vivo)         change from unmodulated
    1-2 mW/cm2                                                  fields; maximum
    (closed irradiation                                         rate of efflux
    system)                                                     at 11 Hz and alterations
                                                                in neuron firing 
                                                                patterns at intensity
                                                                equivalent to 10 mW/cm2
                                                                free field exposure.

    ELF fields,             cerebral          isolated chick    Suppression in                Bawin &
    1-75 Hz; 0.5            Ca+2              and cat           Ca+2 release                  Adey (1976)
    to 1 V/cm               efflux            cerebral          from neurons;
    (closed system                            tissue            biphasic intensity &
    irradiation)                              (in vivo)         frequency dependence;
                                                                maximum effect at
                                                                6 and 16 Hz; 0.1 and
                                                                0.56 V/cm.

    1.5 and 2.45 GHz,       electrical        aplysia ganglia   Effects attributed to         Wachtel et al.
    cw and pw (closed       activity of       (in vivo)         ganglionic warming,           (1975)
    irradiation system)     individual                          but effects not produced
                            neurons                             by non-radiation heating.
                                                                                                                 

    Table 15 (Cont'd)
                                                                                                                 

    Independent             Dependent         Experimental
    variables               variables         subject           Results and comments          Reference
                                                                                                                 

    2.45 GHz, cw            functional        spinal cord of    Alteration in evoked          Taylor &
                            alterations       cat               potentials also produced      Ashlemen, (1975)
                            in neuronal       (in vitro)        by non-radiation
                            elements                            heating but
                                                                with change in timing.

    3 GHz, pw;              electrical        rat               10-day exposure resulted      Servantie et al.
    5 mW/cm2; pulse         activity of       (in vivo)         in synchronization            (1975)
    repetition rate         cortical                            of electronic
    500-600 Hz              neurons                             frequency; synchronization
    (free field                                                 persisted for
    exposure)                                                   hours after exposure.

    2.45 GHz, cw,           synaptic          rabbit vagus      No changes other              Chou & Guy
    0.3-1500 mW/g,          transmission;     nerves, superior  than those thermally-         (1975)
    pw; 0.3-2.2            neural function   cervical          induced.
    1055 mW/g                                 ganglia; rat
    temperature                               diaphragm
    controlled                                muscle
    exposure (closed                          (in vitro)
    system irradiation)

    3.1 GHz; pw             axonal transport  rabbit vagus      No effects.                   Paulsson et al.
    10-400 W/kg             & microtubules    nerve & brain                                   (1977)
    Mean 5  104 to                           extracts
    2  106 W/kg peak                         (in vivo)
    temperature controlled
    exposure
    (free space irradiation)
                                                                                                                 

    Table 15 (Cont'd)
                                                                                                                 

    Independent             Dependent         Experimental
    variables               variables         subject           Results and comments          Reference
                                                                                                                 

    decimeter waves;        neurotransmitter  rabbit            Decreased acetyl-             Syngajevskaja,
    0.5 mW/cm2 (free        release           (in vivo)         cholinesterase (ACHE)         et al. (1962)
    space irradiation)                                          activity.

    10 cm. 0.5 mW/cm2       neurotransmitter  rabbits &         No alteration caused          Baranski (1967)
    (free space             release           guineapigs        by 8-month exposure
    irradiation)            in brain          (in vivo)         to 1 mW/cm2; with
                                                                3-h exposure to 3.5
                                                                mW/cm2, no cw
                                                                effect but pw decreased
                                                                AChE activity
                                                                in guineapigs; after
                                                                4 months exposure,
                                                                there was a decrease
                                                                with cw and an
                                                                increase with pw;
                                                                midbrain most affected;
                                                                lipid & nucleoprotein
                                                                metabolism altered in
                                                                rabbit.

    1.6 GHz; 80             neurotransmitter  rats              10-min exposure led           Merrit et al. (1976)
    mW/cm2 environmental    release           (in vitro)        to 4 C rectal temperature
    temperature             in brain                            rise in irradiated
    (free space                                                 and heated controls;
    irradiation)                                                hypothalamic evarternol
                                                                (nore-pinephrine)
                                                                decreased in both groups; 
                                                                serotonin decreased in
                                                                hippocampus of irradiated 
                                                                animals only.
                                                                                                                 

    Table 15 (Cont'd)
                                                                                                                 

    Independent             Dependent         Experimental
    variables               variables         subject           Results and comments          Reference
                                                                                                                 

    1.7 GHz, cw;            histological      Chinese           30-120 min exposure           Albert &
    10 and 25 mW/           alterations       hamster           led to cytopethological       DeSantis (1975)
    cm2 (free space         in brain          (in vitro)        effects In hypothalamic
    irradiation)                                                and subthalamic neurons; no
                                                                effect on other brain
                                                                regions or on glial
                                                                cells; no repair evident
                                                                dent 14 days after
                                                                exposure.

    960 MHz, cw;            heart rate        isolated          Bradycardia due to            Tinney et al.
    2-10 mW/g (closed                         turtle heart      alteration in neuro-          (1976)
    system irradiation)                       (in vitro)        transmitter release;
                                                                biphasic intensity
                                                                response.

    10.5 cm, cw;            passive and       skeletal          Differential effect           Portela et al.
    0.5-10 mW/cm2;          dynamic           muscle, South     of microwave exposure         (1975)
    temperature-controlled  electric          American frog     on dependent
    exposure (free          parameters        (in vivo)         variable time constants;
    space irradiation)                                          muscle cells of summer 
                                                                frogs more sensitive than 
                                                                those of winter frogs.

    3 & 10.7 GHz,           behavioural       rat               No effects on spontaneous     Roberti et al.
    cw; 0.-526 mW/          modification      (in vivo)         motor activity.               (1975)
    cm2 408-h exposure      (spontaneous
    (free field             motor activity)
    exposure)
                                                                                                                 

    Table 15 (Cont'd)
                                                                                                                 

    Independent             Dependent         Experimental
    variables               variables         subject           Results and comments          Reference
                                                                                                                 

    9.4 GHz, pw;            behavioural       rat               Control results:              Gillard et al.
    2.3 mW/cm2 &            modification      (in vivo)         decrease in locomotor (1976)
    0.7 mW/cm2 average;     (free field                         activity, & vigilance:
    2 week exposure         spontaneous                         increase in exploratory
    (free field             behaviour)                          activity; exposed
    exposure)                                                   results: increased
                                                                exploratory activity
                                                                (slower than controls);
                                                                increase then decrease
                                                                in vigilance, uniform
                                                                locomotor.

    2.45 GHz, pw;           behavioural       rat               Dose-dependent                Thomas et al.
    5, 10, 15 mW/cm2,       modification      (in vivo)         increase in the               (1975)
    30-min exposures        (fixed                              frequency of premature
    (free field exposure)   consecutive                         switching alteration
                            number switching                    (in the perception).
                            frequency)

    2.45 GHz, cw;           behavioural       rhesus monkey     Vigilance performance         De Lorge (1976)
    4-72 mW/cm2;            modification      (in vivo)         not affected by
    30, 60, 120-min         (auditory                           exposure.
    exposures (free         vigilance
    field exposures)        task)
                                                                                                                 

    Table 15 (Cont'd)
                                                                                                                 

    Independent             Dependent         Experimental
    variables               variables         subject           Results and comments          Reference
                                                                                                                 

    2.45 GHz, cw;           behavioural       rhesus            Convulsions induced           Galloway (1975)
    2-min exposure,         modification      monkey            at 15 and 25 W;
    5-25 W output           (discrimination   (in vivo)         irradiation 40 min/
    (applicator             and repeated                        day for 5 days did
    exposure of             acquisition)                        not produce any
    head)                                                       behavioural effects
                                                                at less than 15 W;
                                                                no low-intensity
                                                                effects.

    9.3 GHz, cw;            amplitude of      rabbit            Atypical arousal phenomena,   Goldstein &
    0.7-2.8 mW/cm2,         cortical brain    (in vivo)         3-12 min after exposure,      Sisko (1974)
    5-min exposure          waves in                            followed in 3-5 min
    (free field exposure)   anaesthseized                       by longer period of
                            animals                             arousal; atypical
                            (pentobarbital)                     behaviour.

    2.45 and 1.7            duration of       rabbit            Dose-dependent analeptic      Cleary &
    GHz, cw & pw;           pentobarbital-    (in vivo)         effect.                       Wangemann (1976)
    5-50 mW/cm2             induced sleeping
    (free field exposure)   time
                                                                                                                 

    Table 15 (Cont'd)
                                                                                                                 

    Independent             Dependent         Experimental
    variables               variables         subject           Results and comments          Reference
                                                                                                                 

    3 GHz, pw;              effects of        mice (in vivo)    Exposure delayed              Servantie et al.
    5 mW/cm2 (free          drugs on CNS      rats (in vivo)    onset of pentetrazol-         (1974)
    field exposure)                           and (in vitro)    induced convulsion
                                                                during first 15 days
                                                                of exposure, reduced
                                                                latency after 15 days;
                                                                decreased susceptibility
                                                                to curare-like
                                                                drugs in in vivo and
                                                                in vitro systems.

    Occupational            CNS drug          human             Altered EEG patterns          Edelwejn &
    microwave &             tolerance         subjects          and convulsions in            Baranski (1966)
    RF exposure             (cardiazole)      (in vivo)         workers with over 3           Baranski &
                                                                years microwave               Edelwejn (1968)
                                                                exposure (similar results
                                                                reported in rabbits).

    occupational            CNS functional    human             Transient subjective          Petrov (1970)
    microwave &             disorders         subjects          complaints during
    RF exposure                               (in vivo)         first year of exposure;
                                                                phasic adaptation
                                                                after 1 year; objective
                                                                symptoms of neurovegetative
                                                                disturbances after 5
                                                                years of exposure
                                                                (acrocyanosis, hyper-
                                                                hydrosis, dermographism, 
                                                                hypotonia tremors.
                                                                                                                 

    Table 15 (Cont'd)
                                                                                                                 

    Independent             Dependent         Experimental
    variables               variables         subject           Results and comments          Reference
                                                                                                                 

    3.1 GHz; pw,            histological      rabbit            Cytopathological effects      Paulsson et al.
    55 mW/cm2, repeated     alterations in    (in vivo)         in the plexiform              (1979)
    or single               retina                              layers of retina,
    1-h exposure                                                no effects on photo-
    (free space                                                 receptors; alterations
    irradiation)                                                persisted for 3 months
                                                                after radiation.
                                                                                                                 

    From: Cleary (1978).
    

    7.5  Effects on the Blood Forming and Immunocompetent Cell Systems

        Studies have been conducted on the effects of microwave radiation
    on blood and the immunocompetent system, but the results are
    frequently contradictory and the reasons for the discrepancies are not
    always easily identified. For example, in 1962, Prausnitz & Susskind
    irradiated 100 mice with 9270 MHz microwaves at 100 mW/cm2 for
    9.5 min daily over a period of 59 weeks and reported an increase in
    white blood cells accompanied by lymphocytosis. It was reported that
    leukaemia occurred in 35% of exposed mice, compared with 10% of the
    controls. However, it appears that no attempt has been made to
    replicate these studies.

        A decrease in erythrocytes, leukocytes, and haemoglobin in mice
    was observed by Gorodeckij, ed. (1964) immediately after exposure to
    10 GHz at 450 mW/cm2 for 5 min, and 1 and 5 days later, while
    recovery was evident after 10 days. The influence of microwaves on the
    response of immunocompetent lymphocytes was investigated in mice by
    Czerski (1975). The animals were exposed to 2.95 GHz microwaves at
    0.5  0.2 mW/cm2 for 2 h per day, 6 days per week for 6 and 12
    weeks. During the 2-h exposure, the animals were deprived of food and
    water and were located in separate cages. After exposure, the animals
    were immunized with antigen and the immune response determined by the
    number of antibody-forming cells in the lymph nodes. Significant
    differences were found between the control group and the group exposed
    for 6 weeks, but not the group exposed for 12 weeks. The author
    attributed this result to adaptation. In nonimmunized irradiated mice
    there was an increased number of lymphoblasts in lymph-node cells, but
    no differences in the number of plasmocytes.

        Blast transformation of human lymphocytes  in vitro was observed
    by Stodolnik-Baranska (1967, 1974) after exposure to 2950 MHz
    microwaves at power densities of 7 and 20 mW/cm2. However,
    Smialowicz (1977) was unable to detect any differences between the
    blastogenic responses of microwave-exposed (2450 MHz, 19 W/kg for
    1-4 h) and control mouse splenic lymphocytes activated with various
    mitogens  in vitro.

        The effects on haemopoietic-stem cells in mice of exposure to
    2.45 GHz microwaves at 100 mW/cm2 for 5 min were investigated by
    Kotkovsk & Vacek (1975). The response appeared to occur in 2 stages.
    In the first, the number of leukocytes in the blood increased and both
    bone marrow and spleen cell numbers decreased for 3-4 days following
    exposure. In the second stage, the number of nucleated cells in the
    spleen and the total number of cells in the femur, as detected by
    incorporation of 59Fe, increased until the twentieth day after
    exposure. The incorporation of 59Fe in the spleen decreased to 78%
    of the control value 24 h after exposure and increased to 50% after 14
    days.

        When Lin et al. (1979) studied the effects on mice of single and
    repeated exposures to 148 MHz radiation at 1 mW/cm2 for 1 h per day,
    5 days per week for ten weeks, they did not find any significant
    changes in the blood.

        In studies on 3 strains of rats, a 7-h exposure to 24 GHz
    microwave radiation at 20 mW/cm2 induced significant leukocytosis,
    lymphocytosis, and neutrophilia with recovery in 1 week; after a
    10-min exposure at 20 mW/cm2 or a 3-h exposure at 10 mW/cm2,
    recovery occurred in 2 days (Deichman et al., 1964). The changes
    observed were strain-dependent because in 2 strains the number of
    leukocytes, erythrocytes, and neurophiles increased, while in one
    strain it decreased.

        Decreases in lymphocytes, erythrocytes, and leukocytes, and
    increases in granulocytes and reticulocytes were observed in rats by
    Kitsovskaja (1964) after 3 GHz exposure at 40 mW/cm2 (15 min per day
    for 20 days) and 100 mW/cm2 (5 min per day, for 6 days). Exposure at
    10 mW/cm2 (1 h per day for 216 days) resulted in decreases in total
    WBC and lymphocytes and an increase in granulocytes with no changes in
    other blood components. However, in a study on rats exposed to 2.4 GHz
    microwaves at 5 mW/cm2 (1 h per day for 90 days), Djordjevic et al.
    (1977) did not observe any significant differences in the haematocrit,
    mean cell volume, and haemoglobin between the exposed and control
    groups during 90 days of exposure and for 30 days afterwards.
    Furthermore, there were no significant differences in the number of
    leukocytes, erythrocytes, lymphocytes, and neutrophiles.

        Smialowicz et al. (1977) completed a comprehensive study on rats
    chronically exposed to 425 MHz radiation at 10 mW/cm2 (SAR,
    3-7 mW/g) and to 2.45 GHz radiation at 5 mW/cm2 (SAR, 1-5 mW/g). The
    rats were exposed  in utero and for the first 40 days of life for 4 h
    per day. The only change in the haemopoietic or immunocompetent
    systems was observed in the response of lymphocytes to mitogen.

        The effects on guineapigs and rabbits of prolonged intermittent
    exposures to 3 GHz radiation at 3.5 mW/cm2 for 3 h per day over
    3 months were investigated by Baranski (1971). Increases in absolute
    lymphocyte counts in peripheral blood, and abnormalities in nuclear
    structure and mitosis in erythroblast cells in the bone marrow, and in
    lymphoid cells in lymph nodes and spleen, were found. Rabbits exposed
    at 3 mW/cm2 (2950 MHz continuous and pulsed) for 2 h per day, for 27
    and 79 days showed a decrease in erythropoiesis, as determined by
    59Fe uptake. Pulsed radiation was found to be more effective than
    continuous radiation at the same power level (Czerski et al., 1974a).

        The effects on blood serum in rabbits exposed to 2.45 GHz
    continuous and pulsed radiation at 5, 10, and 25 mW/cm2 for 2 h were
    investigated by Wangemann & Cleary (1976). Changes in the blood
    chemistry of animals irradiated at the three power densities were

    found to be consistent with a dose-dependent response to thermal
    stress. Out of the ten serum components that were analysed,
    statistically significant increases were observed in serum glucose,
    blood urea nitrogen, and uric acid. Dose-dependent transient increases
    returned to normal levels during the week following exposure. No
    differences in the animal's responses to cw and pulsed radiations
    (10-micro-second duration, peak power 485 mW/cm2) were found at the
    same average power density.

        Dogs were exposed to 1285 MHz, 2.8 GHz and 24 GHz at power
    densities between 20 and 165 mW/cm2 (Michaelson et al., 1964, 1971).
    Following exposure to 1285 MHz radiation at 100 mW/cm2 for 6 h, a
    marked increase in leukocytes and neutrophils was found. After 24 h,
    the neutrophil count continued to increase but the lymphocyte and
    eosinophil counts decreased. Neutrophil counts after exposures at 50
    and 20 mW/cm2 (1285 MHz) did not differ significantly from those of
    control animals. A decrease in lymphocytes was noted after the
    exposures at 100 mW/cm2 and 50 mW/cm2, but not after that at
    20 mW/cm2 (Michaelson et al., 1971). Haematological examination of
    the dogs for 12 months after exposure at 20 mW/cm2 did not reveal
    any end points that differed from the control groups.

        A number of studies are listed in Table 16 with details of
    exposure conditions and results of microwave-induced changes in the
    haemopoietic and immunocompetent cell systems.

        This section on the effects of microwaves on the blood forming and
    immunocompetent cells can be summarized as follows:

        (a) Changes in the red and white blood cell counts seem to depend
    on the dose of microwave energy applied. In most of the studies
    reporting positive findings, the effects seem to result from thermal
    stress.

        (b) Repeated exposures to 5 mW/cm2 or below do not appear to
    affect the peripheral blood picture. Effects reported from exposures
    to 15 mW/cm2 or more, depending on the biological system exposed,
    tend to be reversible following termination of exposure.

        (c) The response of the haemopoietic system to microwave radiation
    is significantly different from that to exposure to elevated ambient
    temperatures, even when both result in the same increase in rectal
    temperature. This can be attributed to the nonuniform deposition of
    microwave energy in the body, and the greater depth and rate of
    heating.

        (d) There is evidence that lymphocyte stimulation and effects on
    response may occur under certain experimental conditions, especially
    after exposure to pulsed radiation for repeated or prolonged periods
    at sufficiently high power densities.


        Table 16.  Microwave-induced effects induced in the blood-forming and immunocompetent cell systemsa
                                                                                                                 

    Radiation    Intensity     Exposure
    Frequency    (mW/cm2)      duration          Species        Results                            Reference
    (GHz)
                                                                                                                 

    3            1,5           15,30             granulocyte    Liberation of hydrolases           Szmigielski
                                                 cells          (1 mW/cm2) cell death              (according to
                                                 in culture     (5 mW/cm2; 60 min)                 Cleary (1978))
                                                                lysosomal enzyme release
                                                                (5 mW/cm2; 60 min).

    2.95         0.5           2 h/day for       mouse          Lymphoblasts in lymph              Czerski
                               8 days/week                      nodes, lymphoblastoid              (1975 b)
                               for 6 and/                       transformation during first
                               2 weeks                          2 months and 1 month
                                                                after exposure.

    2.45         100           5 min             mouse          Leukocyte (2 maxima) total         Rotkowska &
                                                                cell volume in the bone            Vacek (1975)
                                                                marrow end spleen, 59Fe
                                                                Incorporation into spleen,
                                                                nucleated cells in spleen
                                                                immediately after exposure
                                                                total cell number in femur
                                                                5-7 days after exposure.
                                                                Colony forming unit numbers
                                                                of stem cells, return
                                                                to normal 12 h after
                                                                exposure.
                                                                                                                 

    Table 16 (Cont'd)
                                                                                                                 

    Radiation    Intensity     Exposure
    Frequency    (mW/cm2)      duration          Species        Results                            Reference
    (GHz)
                                                                                                                 

    3.0          3.5           4 h/day           rat            Leukocyte, altered nuclear         Baranski
                                                                structure, altered mitotic         (1971)
                                                                activity in erythroblasts,
                                                                bone marrow cells &
                                                                lymphatic cells in lymph
                                                                nodes & spleen.

    24           220,10        varied            rat            Leukocyte lymphocyte               Deichman
                                                                neutrophil, all cell counts        et al. (1959)
                                                                returned to normal in
                                                                7 days.

    2.95         3             2 h/day for       rabbit         Erythrocyte production             Czerski et al.
                               37 days                          alterations in circadian           (1974 a)
                               pw & cw,                         rhythms in haemapoietic
                               2 h/day for                      cell mitosis.a
                               79 days cw

    2.45         3,10,25       2 h               rabbit         Serum glucose blood urea           Cleary &
                                                                nitrogen, uric acid, all           Wangemann
                                                                values return to normal            (1978)
                                                                7 days after exposure.

    1.28,        100-165       7 h               dog            Maximum increase in 59Fe           Michaelson
    2.8                                                         incorporation 45 days              et al. (1951)
                                                                after exposure.
                                                                                                                 

    a  From: Bramall (1971).
    

    7.6  Genetic and Other Effects in Cell Systems

        Investigations of biological systems such as cells in culture are
    conducted to gain an understanding of basic mechanisms of interaction.
    Although, these systems are less complex and the dosimetry can be
    better quantitated than in animal studies, the results have to be
    interpreted carefully in assessing potential health hazards to man.

        Microwave exposure has been reported to produce chromosomal
    aberrations (Janes et al., 1969; Mykolajkzyk, 1970; Yao & Jiles, 1970;
    Baranski et al., 1971; Yao, 1971; Czerski et al., 1974b) and mitotic
    alterations (Baranski et al., 1969; Mykolajkzyk, 1970; Baranski et
    al., 1971; Baranski, 1972; Czerski et al., 1974) in cells.

        Yao & Jiles (1970) studied the effects of microwave radiation on
    cell proliferation and on the induction of chromosomal aberrations in
    cultured rat kangaroo cells. Cells were exposed to 2.45 GHz radiation
    in the near field at 1 W/cm2 and 5 W/cm2 and in the far field at
    0.2 W/cm2. Exposure to 0.2 W/cm2 for 1 min caused increased cell
    proliferation, but after 30 min, it decreased. Exposure at higher
    power densities significantly reduced the rate of proliferation,
    Exposure at 5 W/cm2 induced chromosomal aberrations, but it is
    evident that high temperatures were involved in this result, since the
    energy absorption rate measured was 15.2 mW/g.

        Chromosomal aberrations and changes in the duration of particular
    phases of mitosis (mitotic abnormalities) were reported by Baranski et
    al. (1969, 1971) in human lymphocyte cultures and cultures of monkey
    kidney cells following exposures at 3 and 7 mW/cm2 to 10 cm pulsed
    and cw microwaves. Mitotic disorders in the lymphocytes of guineapigs
    and rabbits were also found following exposure to 3 GHz at
    3.5 mW/cm2 for 3 h per day over 3 months (Baranski, 1972).

        Manikowska et al. (1979) studied 16 mice subjected to 9.4 GHz
    pulsed (width 0.5 s, repetition rate 1000 Hz) microwaves at power
    densities of 0.1, 0.5, 1.0 and 10 mW/cm2 for 1 h/day for 2
    consecutive weeks (5 days/week). Disturbances in meiosis were detected
    at power density levels as low as 0.1 mW/cm2. This study needs
    confirmation since no other studies on effects of microwaves on
    meiosis could be found.

        Exposure of murine splenic lymphocytes  in vitro  to 2450 MHz
    radiation at 10 mW/cm2 (dose rate of 19 mW/g) did not result in any
    changes in capacity to synthesize DNA (Smialowicz, 1977). This
    technique used to assess blastic transformations of lymphocytes, was
    not the same as that used by Baranski (1972), which may explain the
    discrepancy in results. Elder & Ali (1975) found similarly negative
    results when they exposed mitochondria of isolated rat liver to
    2.45 GHz radiation at 10 and 50 mW/cm2 for 3.5 h. Furthermore, no
    effects were found in oxidation of substrate, electron transport,
    oxidative phosphorylation, or calcium transport.

        The effects of 2450 MHz microwaves and a 43C water bath on normal
    and virus-transformed fibroblasts of mice were compared by Janiak &
    Szmigielski (1977). Short-term heating by both methods resulted in
    reversible changes in the active transport of potassium through the
    cell membrane. Prolonged heating (over 20 min at 32C) caused
    irreversible damage and the membrane became permeable to large
    molecules.

        In another comparative study, Lin & Cleary (1977) did not find any
    differences in the release of potassium ions, haemoglobin levels, and
    the osmotic fragility of the red-cell membrane between samples exposed
    to microwaves at 2.45, 3.0, and 3.95 GHz and conventionally heated
    samples.

        Chinese hamster ovarian cells exposed to 2.45 GHz microwaves or
    treated in a water bath at the same temperature did not show any
    differences in response when cell survival and sister chromatid
    exchanges were the end points (Livingston et al., 1979).

        In studies by Blackman et at. (1975), the colony forming ability
    of  Escherichia coli B was not inhibited by exposure to 1.7 GHz,
    2.45 GHz, 68-74 GHz, and 136 GHz at power densities ranging from 0.3
    to 20 mW/cm2. This was in contrast to an inhibitory effect of
    microwave radiation at 136 GHz previously reported (Webb & Dodds,
    1968). However, in a more recent study of colony-forming ability and
    of alterations in the molecular structure of living  E. coli B, there
    were no changes in colony growth, or in molecular structure or
    conformation after irradiation at frequencies between 2.6 and 4 GHz
    with a specific absorption rate of 20 mW/g (Corelli et al., 1977).

        Thus, it can be concluded that:

        (a) Chromosomal aberrations and mitotic alterations can be
    produced by microwaves at high power densities where thermal
    mechanisms play a definite role. However, as there are many
    conflicting reports, some doubts remain as to whether these effects
    can occur at lower power densities.

        (b) Studies at the cellular and subcellular level are important
    for understanding basic interaction mechanisms. Chromosomal
    aberrations and mitotic alterations are potential early indications of
    biological changes and may reflect a response of specific tissue, but
    not genetic injury in the organism.

        (c) Recent studies on cell proliferation and capacity to
    synthesize DNA indicate that power densities sufficient to produce
    thermal damage are necessary for effects to appear. This is shown by
    experiments comparing the effects of both water baths and microwave
    exposure. Exposure of animals to resonant frequencies (e.g., 2450 MHz
    for mice), could be expected to induce effects at low power densities
    because a larger proportion of the incident radiation is absorbed and
    converted into heat.

    7.7  Effects on Reproduction and Development

        Detrimental effects of microwaves on testicular function,
    impregnation, developing embryos, and on offspring have been reported
    in the literature.

        Van Ummersen (1961) exposed 48-h chick embryos to 2450 MHz cw
    microwave radiation through the intact shell. The power density was
    20-40 mW/cm2 and exposures were given for 280-300 min, causing the
    yolk temperature to rise from 37C to 42.5C. Abnormalities which were
    observed appeared to be caused by the inhibition of cell
    differentiation and growth. Development of hind limbs, tail, and
    allantois was suppressed. When control eggs were incubated at 42.5C
    for the same length of time and the temperature of the eggs was the
    same as that of microwave-treated eggs, no abnormalities were found.
    It was concluded that the abnormalities from microwave exposure were
    caused by other than thermal factors.

        Mice were subjected to 2.45 GHz microwaves at the near lethal dose
    rate of 38 mW/g for 10 min per day during the 11th-14th days of
    gestation. There were no increases in fetal mortality or deformations
    in treated animals compared with untreated controls and maze
    performance was the same in both groups (Chernovetz et al, 1975).

        When rats were irradiated between days 1 and 16 of pregnancy with
    27 MHz radiation at power densities that caused the rectal temperature
    to rise to 42C, a variety of teratological effects related to the
    developmental stage of the fetus was found. The effect on the
    development of the rat of repeated exposures  in utero to 2.45 GHz
    radiation at 10 mW/cm2 for 5 h per day from day 3 to day 19 of
    gestation was investigated by Shore et al. (1977). Two groups of
    animals were exposed under different conditions of configuration in
    the field. One group was placed in the exposure field in such a way
    that the long axis of each animal was parallel to the electric field;
    animals of the second group were placed with the long axis parallel to
    the magnetic field (orientation parallel to the electric field results
    in substantially greater absorption of microwave energy). No
    significant differences in litter size were observed between the
    control and irradiated animals. Decreases in body and brain mass were
    observed in animals irradiated with the long axis of the body parallel
    to the electric field.

        Rats were exposed to 2.45 GHz radiation at 10 and 40 mW/cm2 for
    1 h per day during critical periods of gestation, and their functional
    development was studied during the 21-day period to weaning
    (Michaelson et al., 1977a). Offspring of rats exposed at 40 mW/cm2
    showed a significantly higher level of corticosterone during the first
    24 h of life and an increase in levels of thyroxin at 14 and 16 days
    of age. Thyroxin levels tended to be lower in one-week-old rats from
    dams that had been exposed at 10 mW/cm2, but increased during the

    second week of life. Adrenal wet mass and ratios of adrenal-to-body
    mass in 7-day-old rats were significantly higher in irradiated
    animals. The authors suggested that while microwave radiation might
    change the developmental process and accelerate the rate of
    maturation, it might also result in some deficiencies. A similar
    result was found by Johnson et al. (1977) who exposed rats  in utero
    to 918 MHz at 5 mW/cm2 for a total of 380 h and found an increase in
    body mass at birth and an acceleration in the time of eye opening.
    Later a deficiency in avoidance response was observed.

        Repeated exposures to 9.4 GHz at power density levels below
    10.0 mW/cm2 may induce disturbances in spermatogenesis and meiosis
    in mice (Manikowska et al., 1979). However, Cairnie & Harding (1979)
    were unable to find any differences in the sperm counts of mice, after
     in vivo exposure to 2450 MHz radiation at 20-32 mW/cm2 for 4 days
    (16 h/day). Testicular damage was observed in mice exposed to 2450 MHz
    at a power density of 6.5 mW/cm2 for 230 h over a 2-month period
    (Haidt & McTighe, 1973); these positive findings could be explained on
    the basis of a thermal mechanism because 2450 MHz is around the
    resonant frequency for mice.

        Changes in testicular morphology were observed by Varma &
    Traboulay (1975) in mice exposed to 1.7 and 3.0 GHz microwaves at
    10 mW/cm2 for 100 min, and at 50 mW/cm2 for 30-40 min. Both
    Bereznitskaja (1968) and Polozitkov et al. (1961) reported that
    chronic exposure of mice to 3 GHz at 10 mW/cm2 or even lower levels
    resulted in a prolonged estrus cycle, partial sterility, and an
    increased, early mortality of the offspring. However, other research
    workers were unable to find any changes in the reproductive
    performance of dogs exposed to 24 GHz microwaves at 24 mW/cm2 for 33
    and 66 weeks (Deichman et al., 1963) and to 1.28 GHz at 20 mW/cm2
    (Michaelson et al., 1971) or female rats and mice exposed to 3.1 GHz
    at 8 mW/cm2 for prolonged periods of time and to 300 mW/cm2 for a
    short period of time (Shore et al., 1977).

        A comparative study of heating the testes of rats by microwaves
    and in warm water was performed by Muraca et al. (1976). Radiation of
    2.45 GHz was used at 80 mW/cm2 with the exposure time varied to
    maintain the desired temperature within  0.5C. Repeated treatments
    during 5 consecutive days resulted in more damage in microwave-
    irradiated animals. However, it was determined that if non-thermal
    effects occurred, it appeared that microwave-induced heating was
    necessary to produce damage.

        The threshold value for testicular damage in dogs exposed to
    2880 MHz microwaves at more than 10 mW/cm2 for unlimited periods was
    studied by Ely et al. (1964). A temperature of 37C was produced more
    rapidly with exposure to higher power densities. This temperature was
    determined as critical for damage based on a minimal demonstrable
    histological change in the most sensitive animal from the test group.
    The authors pointed out that the changes, including sterility, were
    reversible.

        In summary, microwave radiation can affect reproduction and
    development. Both are particularly sensitive to thermal stress,
    although specific effects that are not attributable to heating cannot
    be excluded. Microwave exposure at power density levels causing
    temperature increases results in testicular lesions, and particularly
    affects spermatogenesis, in experimental animals. These lesions seem
    to be readily reversible unless necrosis occurs. Baranski & Czerski
    (1976) in their review of the subject concluded that no serious
    effects should be expected at power density levels below 10 mW/cm2.
    Substantial differences between thermal effects induced by microwaves
    and by other methods of heating may be attributed to different spatial
    distributions of internal heating and different rates of heating.
    Developmental effects seem to be critically dependent on the time of
    exposure to microwaves making it difficult to compare some of the
    experimental data.

    8.  HEALTH EFFECTS IN MAN

        The available data concerning the health effects of microwave
    radiation in man are insufficient, although some surveys of the health
    status of personnel occupationally exposed to microwaves have been
    carried out. The main difficulty in the evaluation of such information
    is the assessment of the relationship between exposure levels and
    observed effects. As often happens in clinical work, it is difficult
    to demonstrate a causal relationship between a disease and the
    influence of environmental factors, at least in individual cases.
    Large groups must be observed to obtain statistically significant
    epidemiological data. The problem of adequate control groups is
    controversial and hinges mostly on what is considered "adequate"
    (Silverman, 1973; Czerki et al. 1974a; NAS/NRC, 1977).

        In view of the lack of good instrumentation, especially of
    personal dosimeters, the quantitation of exposure during work is
    extremely difficult. This is particularly the case where personnel
    move around in the course of their duties and are exposed to
    stationary and non-stationary fields, and both near- and far-field
    exposures. It is impossible to evaluate within reasonable limits the
    exposure over a period of several years. Consequently, investigation
    of the health status of personnel exposed occupationally to microwaves
    necessitates the examination of large groups of workers exposed for
    various periods, if any statistically valid results are to be
    obtained.

        Observations on the health status of personnel exposed to
    microwaves in the USSR have been discussed in detail in monographs
    edited by Petrov, ed. (1970) and Tjagin (1971).

    8.1  Effects of Occupational Exposure

        Prior to the establishment of safety standards, it had been
    observed in some countries that occupational microwave exposure led to
    the appearance of autonomic and central nervous system disturbances,
    asthenic syndromes, and other chronic exposure effects (Gordon, 1966;
    Marha et al., 1971; Dumanski et al., 1975; Serdjuk, 1977). The
    pathogenesis of these syndromes is controversial, their existence has
    been reported on a number of occasions but often without the level of
    exposure. Another problem with earlier reports is that measurement
    techniques were not properly developed at that time (For a detailed
    discussion see Baranski & Czerski (1976) pp. 153-162). Subjective
    complaints consisted of headaches, irritability, sleep disturbance,
    weakness, decrease in sexual activity (libido), pains in the chest,
    and general poorly defined feelings of in health. On physical
    examination, tremor of fingers with extended arms, acrocyanosis,
    hyperhydrosis, changes in dermographism, and hypotonia were reported
    in the USSR (Gordon, 1966). Similar syndromes were reported in France
    by Deroche (1971) and in Israel by Moscovici et al. (1974).

        Examination of the circulatory function included determination of
    the velocity of propagation of the pulse wave. Various coefficients
    may be calculated and used for the evaluation of vascular tonus and
    the state of the neurovegetative system. This method is widely used in
    the USSR, but seldom elsewhere. Disturbances in the functioning of the
    circulatory system are demonstrable using this method whereas, with
    the exception of signs of bradycardia, no significant findings are
    obtained using electro-, vecto-, and ballisto-cardiography.
    Mechanocardiography demonstrated normal or increased systolic and
    minute heart volume in individuals with hypotonia (Tjagin, 1971).

        Gordon (1966) and her colleagues reported studies on
    occupationally exposed workers who were divided into 3 groups
    according to levels of exposure to microwave radiation:

        (a) Periodic exposure at power densities from 0.1 to 10 mW/cm2
    (and higher) of maintenance personnel and workers, who had been
    employed in repair shops since 1953;

        (b) Periodic exposure at power densities from 0.01 to 0.1 mW/cm2
    of technical maintenance workers, some users of microwave devices, and
    research workers, employed after 1960; and

        (c) Systematic low-level exposure of personnel using various
    microwave devices, mainly radar.

        Functional changes in the nervous and cardiovascular systems were
    reported in the first 2 groups. In the first group, a marked
    disturbance in cardiac rhythm, expressed by variability or pronounced
    bradycardia was reported. In the third group, similar effects were
    observed but symptoms were less evident and easily reversed. Only
    about 1000 individuals were observed over a period of 10 years and
    some doubts exist regarding the exact exposure received by the
    workers.

        Clinical observations on the health status of 2 groups of workers
    occupationally exposed to emissions from various types of radio
    equipment were reported by Sadcikova (1974). The first group consisted
    of 1000 workers exposed to RF radiation at a few mW/cm2, the second
    group, of 180 workers who had been exposed at a few hundredths of a
    mW/cm2 over short periods of time. A control group of 200 was
    matched with respect to sex, age and character of work. The health
    status of both exposed groups was reported to differ considerably from
    that of the controls, with a higher incidence of changes in the
    nervous and cardiovascular systems in the exposed groups.

        In Poland (Siekierzynski, 1974; Czerski et al., 1974c;
    Siekierzynski et al., 1974a, b), a selected group of 841 males, aged
    20-40 years and occupationally exposed to microwaves at power
    densities ranging from 0.2 to 6 mW/cm2, was studied. No relationship

    was found between the level or length of occupational exposure and the
    incidence of disorders or functional disturbances such as organic
    lesions of the nervous system, changes in the translucent media of the
    eye, primary disorders of the blood system, neoplastic diseases or
    endocrine disorders, neurasthenic syndrome, disturbances of the
    gastrointestinal tract, and cardiocirculatory disturbances with
    abnormal ECG.

        A 3-year epidemiological study aimed at determining health risks
    from microwave exposure in US naval personnel was reported by
    Robinette & Silverman (1977). Mortality, morbidity, reproductive
    performance, and health of children were investigated in 20 000
    occupationally exposed subjects and 20 000 controls. No significant
    differences were found between the 2 groups.

        Cases of whole body or partial body overexposure may occur among
    personnel operating high-power equipment. Exposure of the head and
    resultant injury to the brain have been reported (Servantie et al.,
    1978). The person concerned may not realize that exposure is taking
    place, if there is no sensation of heat. The symptoms may appear
    later, and a syndrome of meningitis or symptoms similar to those of
    heat stroke may develop.

        It has been emphasized by many research workers, including
    Silverman (1973), that the inadequacies and uncertainties of radiation
    measurements and exposure data from existing, clinical studies, make
    it impossible to determine if, and under what conditions, microwave
    radiation can induce neural or behavioural changes in man.
    Unfortunately, the same problem exists for other studies carried out
    on human subjects exposed to microwaves, making it difficult to draw
    conclusions on health status.

    8.1.1  Effects on the eyes

        Epidemiological surveys of lenticular effects in microwave workers
    have been performed in Poland (Siekierzynski et al., 1974a, b;
    Zydecki, 1974), Sweden, (Tengroth & Aurall, 1974) and the USA (Cleary
    & Pasternack, 1966; Appleton & McCrossan, 1972; Shacklett et al.,
    1975). No statistically significant increases in the number of
    cataracts in personnel occupationally exposed to microwave radiation
    were observed in any of the surveys. Tengroth & Aurell (1974)
    indicated a statistically significant increase in lenticular defects
    and retinal lesions in 68 workers in a Swedish factory, where
    microwave equipment was tested. These authors were some of the first
    to point out possible retinal lesions from exposure to microwaves.
    However, survey data on the intensity of radiation were not provided
    and the control group was not age-matched. Statistically significant
    differences in lens opacities between exposed and control groups were

    not found in any of the other surveys. In cases of confirmed
    cataracts, there had been reported exposures at densities exceeding
    100 mW/cm2; indeed, power densities as high as 1000 mW/cm2 were
    cited.

    8.1.2  Effects on reproduction and genetic effects

        There is little information on the effects of microwave radiation
    on male or female reproductive functions. Reports of sterility or
    infertility from exposure to microwaves are questionable. No changes
    in the fertility of radar workers were found by Barron & Baraff
    (1958).

        Marha et al. (1971) attributed decreased spermatogenesis, altered
    sex ratio of births, menstrual pattern changes, congenital effects in
    newborn babies, and decreased lactation to the occupational exposure
    of mothers to RF radiation. According to their report, such effects
    occurred at power densities exceeding 10 mW/cm2.

    8.1.3  Cardiovascular effects

        Functional damage to the cardiovascular system as manifested by
    hypotonus, bradycardia, delayed auricular and ventricular
    conductivity, and flattening of ECG waves, has been reported, by
    several USSR clinicians, to result from chronic exposure of workers to
    RF fields (Gordon, 1966, 1967; Tjagin, 1971; Baranski & Czerski,
    1976). Decreases in blood pressure from exposure have also been
    reported. Some authors in the USSR have indicated that the nature and
    seriousness of cardiovascular reactions to prolonged exposure is
    related to changes in the nervous system, and depends on the
    characteristics of the individual. Some patients exhibited only minor
    asthenic symptoms while others developed marked autonomic vascular
    dysfunction.

    8.2  Medical Exposure

        Controlled follow-up studies of patients treated with microwave
    and RF diathermy could yield important data on effects, at least for
    partial body exposure. Such studies could not be found in the
    available literature. However, cases of congenital malformations
    ascribed to exposure to microwave or RF diathermy during early
    pregnancy have been found in the literature by Marha et al. (1971).

    9.  RATIONALES FOR MICROWAVE AND RF RADIATION PROTECTION STANDARDS

    9.1  Principles

        An important part of the rationale for standards should be the
    definition of the population to be protected. Occupational health
    standards are aimed at protecting healthy adults exposed under
    controlled conditions, who are aware of the occupational risk and who
    are likely to be subject to medical surveillance. General population
    standards must be based on broader considerations, including health
    status, special sensitivities, possible effects on the course of
    various diseases, as well as limitations in adaptation to
    environmental conditions and responses to any kind of stress in old
    age. As many of these considerations involve insufficiently explored
    interactions, standards for the general population must involve
    adequate safety factors, including taking into account the possibility
    of 24-h general population exposure compared with 8-h occupational
    exposure.

        A distinction should be made between exposure limits for workers
    and equipment emission standards. The latter are based on safe
    operational considerations, should be derived from exposure limits,
    and they should not allow exposure above the adopted exposure limits.
    The USA performance standard for microwave ovens (US Code of Federal
    Regulations, 1970) may serve as an example. This standard limits the
    emission of unintentional radiation (microwave leakage) to 1 mW/cm2
    at a distance of 5 cm from the surface of the oven. Only a few
    countries have formally adopted standards. Where standards have been
    promulgated, the procedures of enforcement vary from regulations
    enforceable by law to voluntary guidelines.

        Existing radiation protection guides (RPG) or exposure standards
    may be divided into 3 groups according to the exposure limits adopted
    (Czerski, 1976).

        The first group comprises standards and recommendations in which
    microwave exposure of the order of tens of microwatts/cm2 (up to
    100 W/cm2) is allowed. The second group includes exposures of the
    order of hundreds of microwatts/cm2 (1000 W/cm2), and the third
    group allows exposures of thousands of microwatts/cm2
    (10 000 W/cm2). This division does not correspond to any
    classification of RPG or exposure limits on a national or regional
    geographical basis. As exposure standards have been revised or
    introduced they have recently tended towards group 2 (Repacholi,
    1978).

    9.2  Group 1 Standards

        The first group is represented by the exposure standards of
    Bulgaria (Bulgarian National Standard, 1979) and the USSR (Ministry of
    Health of the USSR, 1970; USSR Standard for Occupational Exposure,
    1976; USSR Standard for Public Exposure, 1978).

        The original USSR occupational microwave exposure limits were
    established in 1959 (Ministry of Health of the USSR, 1970). The
    current standard (USSR Standard for Occupational Exposure, 1976)
    reaffirmed the exposure limits for microwaves (300 MHz-300 GHz) and
    introduced exposure limits for RF (60 kHz-300 MHz). A special standard
    was introduced for public exposure in 1978 (USSR Standard for Public
    Exposure, 1978). Detailed data on exposure limits are given in Table
    18 at the end of section 9.5. The exposure limits representative for
    this group of standards are those of the USSR occupational standard
    (USSR Standard for Occupational Exposure, 1976): microwave radiation
    (300 MHz-300 000 MHz) at working locations should not exceed 10
    microwatt/cm2 (0.1 W/m2) for exposure during the whole working
    day, 100 microwatt/cm2 (1 W/m2) for exposures of not more than 2 h
    per working day, and 1000 microwatt/cm2 (10 W/m2) for exposures of
    not more than 15-20 min per working day, providing that protective
    goggles are used and that the radiation (exposure) does not exceed 10
    microwatt/cm2 (0.1 W/m2) during the rest of the working day.

        The principle of establishing exposure levels in standards,
    according to Gordon (1966, 1970), is the avoidance of risks during
    long-term (many years) occupational exposure.

        In the USSR standard concerning general population exposure to
    microwaves in the range of 300 MHz-300 GHz (Fig. 15), a value of
    5 W/cm2 has been adopted as the exposure limit over a 24-h period,
    for inhabited areas. This standard covers radiation from scanning and
    rotating antennae, which turn with a frequency below 0.5 Hz. The
    irradiation time of a point in space should not exceed one tenth of
    the scanning duty cycle, and the relation between the maximum energy
    levels in comparable time intervals should not exceed 10.

        The USSR occupational and public health safety standards are based
    on the principle of complete prevention of health risks and therefore
    include large safety factors.

    9.3  Group 2 Standards

        The second group of standards may be illustrated by those of
    Czechoslovakia (Principal Hygienist of CSSR, 1965, 1970), the German
    Democratic Republic Standard (GDR Standard TgL 32602/01, 1975), the
    Polish regulations on microwave exposure limits (Council of Ministers,
    1972) and RF exposure limits (Ministers of Labour, Wages and Social
    Affairs and Health and Social Welfare, 1977), as well as the USA Bell

    FIGURE 15

    Telephone recommendations (Weiss & Mumford, 1961). The recently
    introduced Canadian (National Health and Welfare, Canada, 1979) and
    Swedish (IVA-Committee, 1976; Worker Protection Authority, 1976)
    exposure standards and the Australian proposal (Cornelius & Vigilione,
    1979) might also be placed in this group.

        The Czechoslovak standard is discussed in detail by Marha et al.
    (1971), who claim that "biological knowledge" was taken into account
    in establishing the permissible exposure levels and a safety factor of
    10 introduced. Ten microwatts/cm2 (0.1 W/m2) mean power density
    was accepted as safe for long-term exposures to pulsed waves. For the
    "demonstrably less risky" continuous wave exposure, 25
    microwatts/cm2 was permitted. These rules were first adopted in 1965
    and were revised in 1970 (Principal Hygienist of CSSR, 1965, 1970) in
    order to incorporate a time-weighted averaging procedure.

        RPG values based on an 8-h working day for occupational exposure
    and over 24-h for the general population have also been introduced.
    For occupational continuous wave exposure to microwaves, the exposure
    limit may not exceed 25 microwatts/cm2. The permissible exposure
    levels are calculated according to a formula from which a continuous
    wave exposure to 1.6 mW/cm2 or pulsed wave exposures to
    0.64 mW/cm2 during 1-h per working day are permissible. This is
    considerably higher than the values accepted in the USSR. No advice is
    given concerning exposure lasting for a few minutes. Details of
    measuring methods and equipment are also given by Marha et al. (1971).
    Continuous generation is defined as operation with a ratio of
    on-to-off time greater than 0.1. The overall impression is that the
    values accepted in Czechoslovakia for short periods of exposure (2 or
    10 min), may be compared with those recommended by the American
    National Standards Institute (ANSI, 1974, 1979).

        Poland adopted the same exposure limits as those of the USSR in
    1961. In 1963, additional information on interpretation was
    introduced. Effective irradiation time was defined by the following
    expression for far-field exposure to intermittent radiation from
    scanning beams:

                          tef = (phi/360)  tp

    where  tef = effective irradiation time (h)
           tp = time of emission of microwaves
          phi = effective beam width in degrees.

    Special formulae were given for the near-field zone. Because of the
    difficulties of solving all the doubts arising out of practical
    situations, new exposure limits were subsequently proposed. These were
    based on detailed discussions of findings in Czechoslovakia, the USSR

    and the USA, radiation protection guides, standards, and rules, and
    epidemiological analysis of the health status of personnel
    professionally exposed to microwaves (Czerski & Piotrowski, 1972). The
    new proposals were accepted and introduced in laws passed in Poland by
    the Council of Ministers (1972) and the Minister of Health and Social
    Welfare (1972) (Fig. 16). For the general population, the values of 10
    and 100 W/cm2 were adopted for continuous and intermittent
    exposures, respectively. These values were taken as the upper limits
    for a safe zone, in which occupation could be unrestricted. Three
    other zones were defined, based on power density. For stationary
    (continuous) fields, these were:

    FIGURE 16

        (a) safe zone -- the mean power density not to exceed 0.1 W/m2,
    human exposure unrestricted;

        (b) intermediate zone -- minimum value 0.1 W/m2, upper limit
    2 W/m2, occupational exposure allowed during a whole working day
    (normally 8 h, but, in principle, could be extended to 10 h);

        (c) hazardous zone -- minimum value 2 W/m2, upper limit
    100 W/m2, occupational exposure time per 24 h to be determined by
    the formula:

                                t = 32/ p2

    where  t = exposure time (h) and  p = mean power density (W/m2);

        (d) dangerous zone -- mean power density in excess of 100 W/m2
    (10 mW/cm2), human exposure forbidden.

        For exposures to non-stationary fields, i.e., intermittent
    exposure, the following values were adopted:

        (a) safe zone -- mean power density not to exceed 1 W/m2
    (0.1 mW/cm2);

        (b) intermediate zone - minimum value 1 W/m2, upper limit
    10 W/m2, occupational exposure allowed during a whole working day,
    as defined earlier;

        (c) hazardous zone -- minimum value 10 W/m2, upper limit
    100 W/m2, the professional exposure time per 24 h to be determined
    by the formula:

                                t = 800/ p2

    where  t = exposure time (h) and  p = mean power density (W/m2);

        (d) dangerous zone -- mean power density in excess of 100 W/m2
    (10 mW/cm2), human exposure forbidden.

        The Polish law (Council of Ministers, 1972) names the bodies to be
    responsible for health surveillance, supervision of working
    conditions, and the manner of carrying out the measurements (in
    principle, every 3 years, and after changes in equipment or its
    displacement). The main responsibility for decisions on admissibility
    of working conditions rests with the sanitary epidemiological stations
    of the Public Health Service. Newly designed equipment must be
    evaluated by the Ministry of Health and Social Welfare, before
    production and/or installation is allowed. For installation of
    microwave equipment, permission is required from the sanitary
    epidemiological station of the province.

        These Polish regulations, in common with those of Czechoslovakia
    and the USSR, have the following characteristics:

        (a) Exposure limits determined separately for occupational and
    general population exposures, medical examinations of microwave
    workers limit occupationally exposed population to healthy adults
    only;

        (b) unified methods of measurement, measuring equipment, and
    evaluation of results for health purposes;

        (c) unified methods of medical examinations and evaluation of the
    results obtained;

        (d) determination of responsibility for compliance with RPG.

        Sweden has introduced regulations for occupational exposure with
    1 mW/cm2 as the normal limit for microwave exposure and allows
    short-term excursions to a maximum of 25 mW/cm2. In the range
    10-300 MHz, the limits are 5 mW/cm2 and 25 mW/cm2 (IVA Committee,
    1976; Workers Protection Authority, 1976).

        A new Canadian standard has now been published (National Health
    and Welfare, Canada, 1979). This standard was developed following an
    in-depth scientific evaluation of the literature (National Health and
    Welfare, Canada, 1977, 1978) and was proposed (Repacholi, 1978) as a
    draft so that it could be extensively reviewed. The final standard
    applies to both occupational exposure and exposure of the general
    population. Table 17 summarizes the exposure limits for whole or
    partial body exposure to either continuous or modulated
    electromagnetic radiation in the frequency range 10 MHz-300 GHz.

        Higher occupational exposure is permitted for periods of less than
    1 h. However, the maximum power density, averaged over a 1-min period
    should not exceed 25 mW/cm2. Fig. 17 shows the permitted
    occupational exposure in Canada.

        Recently, the Australian Radiation Laboratory published a draft
    proposal (Cornelius & Viglione, 1979) for exposure limits in the range
    of 10 MHz-300 GHz. The values proposed are shown in Fig. 18 and,
    according to the authors, are the result of a "worst case analysis".
    Although, the rationale and some of the calculations presented in this
    paper may be questioned on a formal basis, it is interesting to note
    that the values for exposure limits agree well with those of the group
    2 of standards.

    FIGURE 17

    FIGURE 18

    Table 17.  Canadian exposure limits for whole or partial
               body exposure continuous or intermittent radiation
               from 10 MHz-300 GHza
                                                                

    Group               Frequency range        Exposure limits
                                                                

    General             10 MHz--300 GHz           1 mW/cm2
    population                                     60 V/m
                                                  0.16 A/m
                                             Averaged over 1 min

    Occupational        10 MHz--1 GHz             1 mW/cm2
                                                   60 V/m
                                                  0.16 A/m
                                              Averaged over 1 h

                        1 GHz--300 GHz            5 mW/cm2
                                                   140 V/m
                                                  0.36 A/m
                                              Averaged over 1 h
                                                                

    a  From: National Health and Welfare, Canada (1979).


    9.4  Group 3 Standards

        The third group of standards may be illustrated by the 1966 US
    Army regulations (Polmisans & Peczenik, 1966), The American National
    Standards Institute Standard (ANSI, 1966) and recommendations of the
    American Conference of Governmental Industrial Hygienists (ACGIH,
    1971, 1979). Fig. 19 presents a comparison of these standards with the
    Bell Telephone recommendations (Weiss & Mumford, 1961).

        The US Army Standard is obviously intended as an occupational
    safety RPG to microwaves and RF. Unlimited exposure is allowed at
    levels below 10 mW/cm2 but exposure at power densities higher than
    100 mW/cm2 is considered dangerous. Within the range of
    10-100 mW/cm2, exposure is allowed for a limited time according to
    the formula:

                              t = 6000/ Pd2

    where  t = exposure time (min) and

           Pd = mean power density (mW/cm2).

    FIGURE 19

        A practical upper limit of 55 mW/cm2 is imposed, based on the
    assumption that exposure of less than 2 min duration cannot be
    properly regulated.

        It is also recommended that, wherever possible, exposure levels
    inside military installations should be reduced to a minimum.

        The recommendations drawn up by the C-95.1 Committee of the
    American National Standards Institute do not set an upper limit of
    exposure (ANSI, 1966). However, this limit is defined indirectly by
    the recommendation that the power density to which people may be
    exposed should not exceed 10 mW/cm2 as averaged over any period of
    0.1 h. No distinction between pulsed or continuous wave exposure is
    made. These recommendations allow a 1-min exposure to 60 mW/cm2,
    which may be repeated 10 times per hour. US Army recommendations allow
    only a single 2-min exposure at 55 mW/cm2 during 1 h. On the other
    hand, ANSI recommendations allow a 6-min exposure at only 10 mW/cm2,
    while the US Army accepts 32 mW/cm2 for this period.

        The ANSI C.95.1 Committee revised its standard in 1974 (ANSI 1974)
    and is considering a draft proposal to reduce the permissible exposure
    limits (ANSI, 1979). A comparison of the ANSI exposure limits in
    successive standards can be found in Table 18 at the end of this
    section.

        The American Conference of Governmental Industrial Hygienists has
    also made recommendations for the frequencies of 300 MHz-300 GHz
    (ACGIH, 1971, 1979, 1980):

        (a) For average power density levels up to, but not exceeding
    10 mW/cm2, total exposure time should be limited to the 8-h working
    day (continuous exposure).

        (b) Exposure to higher average power density levels is permitted
    for short periods of time. For example, exposure to 25 mW/cm2 is
    permitted for 2.4 min during each 6-min period in an 8-h working day
    (intermittent exposure);

        (c) For average power density levels exceeding 25 mW/cm2, no
    exposure is permissible (ceiling value).

        (d) Under conditions of moderate to severe heat stress, the values
    recommended may need to be reduced.

        These Group 3 recommendations are based on human thermal balance
    characteristics contained in the studies by Schwan & Piersol (Schwan,
    1978; Schwan & Piersol, 1954, 1955) on the biophysical and
    physiological aspects of the absorption of electromagnetic energy in
    body tissues. These views (Schwan, 1976) can be presented briefly as
    follows:

        (a) the principal effects of microwaves consist of temperature
    increases in the irradiated object;

        (b) because of heat balance characteristics in man, indefinite
    exposure to 10 mW/cm2 is possible, higher values may be accepted for
    short-term exposure;

        (c) the formation of cataracts or lenticular opacities cannot be
    expected at power densities below 100 mW/cm2;

        (d) biophysical considerations exclude the possibility of
    microwave interaction with nerve cells;

        (e) there is no evidence of untoward effects of microwave
    radiation in man at power densities below 10 mW/cm2.

        The US ANSI Committee is in the process of revising its standard
    and it appears likely from review documents, which have been
    circulated, that the 10 mW/cm2 value will be reduced to 1 mW/cm2
    in the frequency range 30-300 MHz with increased levels on either side
    of this frequency range (ANSI, 1979). This standard would then come in
    Group 2.

    9.5  RF Radiation Standards (100 kHz to 300 MHz)

        The USA exposure limits covering the range 10 MHz-100 GHz and some
    other national standards (e.g., the United Kingdom) include a part of
    the RF range. Standards intended specifically for RF radiation (as
    defined by international agreement), have been introduced only in
    Czechoslovakia (Principal Hygienist of CSSR, 1965, 1970), the German
    Democratic Republic (GDR Standard -- TGL 32602, 1973), Poland
    (Ministers of Labour, Wages and Social Affairs and of Health and
    Social Welfare, 1977), and in the USSR (USSR Standard for Occupational
    Exposure GOST 12.1.00.76, 1976; USSR Standard for Public Exposure
    SN-1823-78, 1978).

        In the USSR occupational standard, values from 5 V/m to 50 V/m
    have been adopted in the range of 60 kHz to 300 MHz (see Table 18).
    The USSR values for inhabited areas (public health standards) are as
    follows:

                                         E field

        in the range of 30--300 kHz      20 V/m

        in the range of 0.3-- 3 MHz       10 V/m

        in the range of  3-- 30 MHz        4 V/m

        in the range of 30--300 MHz        2 V/m

        In the Czechoslovak standard (Marha et al., 1971), the approach to
    RF exposure is similar to that for microwave exposure. The permissible
    exposure duration for the frequency range 30 kHz-30 MHz is calculated
    from the formula:

                                E   t = 120

    where  E = peak electric field strength (V/m)
           t = time (h)

        For 24-h exposure, 5 V/m is considered safe. In the range of
    30 MHz-300 MHz, the equivalent is 1 V/m.

        Occupational exposure guide values are: 400 for 40 kHz-30 MHz and
    80 for the range 30 MHz-300 MHz allowing 50 V/m and 10 V/m,
    respectively, for an 8-h working day.

        The Polish proposal uses the concept of 4 zones, i.e., safe,
    intermediate, hazardous, and dangerous, and exposure limits presented
    in Fig. 20 and 21 are of the same order of magnitude as those for
    Czechoslovakia and the USSR.

        Table 18 includes examples of microwave and RF exposure limits
    adopted or proposed by various countries.

    FIGURE 20

    FIGURE 21


        Table 18.  Examples of microwave and RF exposure limits in various countries
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

     Australia

    Australian        Draft proposal                     Frequency (f) MHz dependent      24 h            both    both         Compare Fig. 18;
    Radiation         for both                           limit (L) mWh/cm2 for time                                            a proposal for
    Laboratory        occupational                       integrated exposures average                                          near-field
    (Cornelius &      and public                         over any 1-h period                                                   exposure limits
    Viglione,         exposure                           and 4 (L) mW/cm2 averaged                                             is also included,
    1979)                                                over any 1-s period for                                               peak pules
                                                         periods of less than 1 h                                              exposure is
                                                                                                                               limited to
                                                                                                                               1 W/cm2.

                                      10-30 MHz          L = 5.4 - 0.365 f + 0.0064 f2
                                      30-130 MHz         L = 0.2
                                      130-600 MHz        L = 0.2 + 0.00128 (f + 130)
                                      0.6-3 GHz          L = 0.8 + 0.00029 (f + 600)
                                      3-300 GHz          L = k.5

     Bulgaria

    State             Legal national                     Electric field strength V/m
    (National)        standards;      60 kHz-3 MHz       50 V/m                           working day     -       -
    Committee for     enforceable     3 MHz-30 MHz       20 V/m                           working day
    standardization   by law;         30 MHz-50 MHz      10 V/m                           working day
    (1979)            occupational    50 MHz-300 MHz     5 V/m                            working day
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

                                                         Magnetic field strength A/m      working day
                                      60 kHz-1.5 MHz     5 A/m                            working day
                                      30 MHz-50 MHz      0.3 A/m                          working day
                                                         Power density W/m2               working day

                                      300 MHz-300 GHz    up to 0.1                        working day     both    stationary
                                      300 MHz-300 GHz    0.1-1 W/m2                       no more than    both    stationary   Up to 0.1 during
                                                                                          2 h                                  the remainder
                                                                                                                               of the working
                                                                                                                               day.

                                      300 MHz-300 GHz    1.0-10.0 W/m2                    no more than    both    stationary   Up to 0.1 during
                                                                                          20 min                               the remainder of
                                                                                                                               the working day-
                                                                                                                               protective goggles
                                                                                                                               required.

                                      300 MHz-300 GHz    up to 1.0 W/m2                   working day     both    rotating
                                      300 MHz-300 GHz    1.0-10.0 W/m2                    no more than    both    rotating     If the ambient
                                                                                          2 h                                  temperature is
                                                                                                                               over 28 C or
                                                                                                                               simultaneous
                                                                                                                               exposure to
                                                                                                                               X-rays occurs,
                                                                                                                               exposures over
                                                                                                                               1.0 W/m2 are
                                                                                                                               not allowed.
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

     Canada

    Canadian          Voluntary,      10 MHz-100 GHz     10 mW/cm2                        no limit        cw      both         No longer applies,
    Standards         occupational                                                                                             as the 1979
    Association                                                                                                                national standard
    (1966)                                                                                                                     is more
                                                                                                                               conservative.
                                                         1 mWh/cm2                        0.1 h           pulsed  both

    National          National
    Health &          health and
    Welfare           occupational
    (1979)            safety
                      regulation,
                      enforceable by
                      law.
                      Occupational    10 MHz-1 GHz       1 mW/cm2 power density           no limit        both    both         See also Fig. 17.
                                                         60 V/m rms electric field        averaged
                                                         strength                         over 1 h
                                                         0.16 A/m rms magnetic field
                                                         strength
                                      1 GHz-300 GHz      5 mW/cm2 power density           averaged over   both    both
                                                         140 V/m rms electric field       1 h
                                                         strength
                                                         0.36 A/m rms magnetic field
                                                         strength
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

                                      10 MHz-300 GHz     25 mW/cm2 power density          1 min           both    both         These values
                                                         300 V/m rms electric field                                            cannot be exceeded
                                                         strength                                                              and constitute
                                                         0.8 A/m rms magnetic field                                            "ceiling levels".
                                                         strength                                                              Some provisions
                                                                                                                               for "special"
                                                                                                                               cases, under
                                                                                                                               strictly
                                                                                                                               controlled
                                                                                                                               conditions were
                                                                                                                               added. 10 mW/cm2
                                                                                                                               cannot be exceeded
                                                                                                                               when averaged over
                                                                                                                               1-h period.
                      General         10 MHz-300 GHz     1 mW/cm2 power density           no limit,
                      population                         60 V/m rms electric field        averaged
                                                         strength                         over 1 min
                                                         0.16 A/m rms magnetic field
                                                         strength

     Czechoslovakia

    Principal         National
    Hygienist         health and
    of the CSSR       occupational
    (1970)            safety
                      regulation
                      enforceable
                      by law
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

                      Occupational    30 kHz--30 MHz     Exposure limit (L) V/m           Exposure        -       -            Occupationally
                                                         calculated according to          duration (t)                         exposed persons
                                                         formula:                         in hours                             are under
                                                         L  t (h) = 400, i.e., 50 V/m    calculated                           obligatory medical
                                                         for 8 h                          according to                         surveillance
                                      30 MHz--300 MHz    L  t (h) = 80, i.e., 10 V/m     the formula in                       (periodical
                                                         for 8 h                          the next column                      examinations as
                                                                                          to the left                          specified by law).
                                      300 MHz--300 GHz   Exposure limit (L) W/cm2                                             Unified measuring
                                                         calculated according to                                               methods imposed
                                                         formula L  t (h) = 200 i.e.,                                         and specified by
                                                         25 W/cm2 for 8 h                as above        cw      both         the same
                                                                                                                               regulations. The
                                      300 MHz--300 GHz   L  t (h) = 80, i.e., 10 W/                                          regulations dated
                                                         cm2 for 8 h                      as above        pulsed  both         1965 limited peak
                                                                                                                               pulse power
                      General         30 kHz--30 MHz     Exposure limit (L) V/m           as above        --      --           (instantaneous
                      population                         calculated according to                                               exposure) to 1 kW/
                                                         formula L  t (h) = 120,                                              omitted in the
                                                         i.e., 5 V/m for 24 h                                                  revision dated
                                      30 MHz--300 MHz    Exposure limit (L) V/m           as above        -       -            1970.
                                                         calculated according to
                                                         the formula L  t (h) = 24.
                                                         i.e., 1 V/m for 24 h
                                      300 MHz--300 GHz   Exposure limit (L) W/cm2        as above        cw      both
                                                         calculated according to the
                                                         formula L  t (h) = 60.
                                                         i.e., 2.5 W/cm2 for 24 h
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

                                      300 MHz--300 GHz   L  t (h) = 24, i.e., W/        as above        pulsed  both
                                                         cm2 for 24 h

     German Democratic Republic

    National          National        60 kHz--3 MHz      50 V/m electric field strength   working day     _       _            Supersedes a
    Committee         occupational    3 MHz--30 MHz      20 V/m electric field strength   working day     _       _            standard dated
    for               health          30 MHz--50 MHz     10 V/m electric field strength   working day     --      --           1972, microwave
    Standardization,  standards,      50 MHz--300 MHz    5 V/m electric field strength    working day     --      --           exposure limits
    Measurements      enforceable     300 MHz--300 GHz   10 W/cm2 power density          up to 8 h       both    stationary   did not change,
    and Products      by law          300 MHz--300 GHz   100 W/cm2 power density         up to 2 h       both    stationary   RF exposure limits
    Control (1975)                    300 MHz--300 GHz   1000 W/cm2 power density        up to 20 min    both    stationary   were introduced
                                                                                                                               by the new
                                                                                                                               version.
                                      300 MHz--300 GHz   100 W/cm2 power density         up to 8 h       both    rotating
                                      300 MHz--300 GHz   1000 W/cm2 power density        up to 2 h       both    rotating     1000 W/cm2 is a
                                                                                                                               "ceiling level"
                                                                                                                               that cannot be
                                                                                                                               exceeded.

     Poland

    Council of        National        300 MHz--300 GHz   up to 0.1 W/m2 (safe zone)       unlimited       both    stationary   Supersedes a 1961
    Ministers         regulation,                                                         (implicit                            regulation
    (1972)            enforceable                                                         general public)                      establishing
                      by law                                                                                                   essentially the
                                                                                                                               same exposure
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

                                      300 MHz-300 GHz    0.1 W/m2-2 W/m2                  working day     both    stationary   limits, as those
                                                         (intermediate zone)                                                   in the USSR.

                                      300 MHz-300 GHz    2 W/m-100 W/m2                   32 hours        both    stationary   Although an
                                                         (hazardous zone)                 P2                                   occupational
                                                                                                                               standard. It
                                      300 MHz-300 GHz    Exceeding 100 W/m2               human           both    stationary   established a
                                                         (danger zone)                    occupancy                            "safe" zone,
                                                                                          prohibited                           within which
                                                                                          betide (ceiling                      human occupancy
                                                                                          level)                               is unrestricted.
                                      300 MHz-300 GHz    up to 1 W/m2 (safe zone)         unlimited       both    rotating     Only workers
                                                                                          (implicit                            (persons
                                                                                          general public)                      occupationally
                                                                                                                               exposed) having a
                                                                                                                               medical
                                                                                                                               certificate of
                                                                                                                               fitness and
                                      300 MHz-300 GHz    1 W/m2-10 W/m2                   working day     both    rotating     subject to
                                                         (intermediate zone)                                                   periodic medical
                                                                                                                               examinations may
                                                                                                                               enter the
                                                                                                                               "intermediate"
                                      300 MHz-300 GHz    10 W/m2-100 W/m2                 800 hours       both    rotating     and "hazardous"
                                                         (hazardous zone)                 P2                                   zones. In this
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

                                      300 MHz-300 GHz    Exceeding 100 W/m2               human occupancy both    rotating     way an implicit
                                                         (danger zone)                    prohibited                           general population
                                                                                          (ceiling                             exposure limit has
                                                                                          level)                               been established.
                                                                                                                               A regulation
                                                                                                                               establishing
                                                                                                                               general public
                                                                                                                               and environmental
                                                                                                                               protection
                                                                                                                               exposure limits
                                                                                                                               for microwave, RF,
                                                                                                                               and ELF was
                                                                                                                               drafted and will
                                                                                                                               be adopted in
                                                                                                                               1980. Compare
                                                                                                                               Fig. 16 and
                                                                                                                               section 9.3.
                                                                                                                               Occupational
                                                                                                                               exposure durations
                                                                                                                               and definitions of
                                                                                                                               electromagnetic
                                                                                                                               fields, stationary
                                                                                                                               versus rotating
                                                                                                                               antennae,
                                                                                                                               determined by a
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

                                                                                                                               separate
                                                                                                                               regulation
                                                                                                                               (Minister of
                                                                                                                               Health
                                                                                                                               & Social Welfare,
                                                                                                                               1972). P = power
                                                                                                                               density W/m2.

    The Ministers     National        0.1 MHz-10 MHz     20 V/m rms electric field        unlimited       --      --           The same concept
    of Labour,        regulation                         strength (safe zone)             (implicit                            of safe,
    Wages and         enforceable                                                         general                              intermediate,
    Social Affairs    by law                                                              population)                          hazardous, &
    and for Health                                                                                                             danger zones makes
    and Social                                           20 V/m-70 V/m rms electric       working day     both    _            the standard an
    Welfare (1977)                                       field strength (intermediate                                          implicit general
                                                         zone)                                                                 population one.
                                                                                                                               Within the 0.1-
                                                                                                                               10 MHz range, rms
                                                         70 V/m-1000 V/m rms electric     560             both    rotating     magnetic field
                                                         field strength (hazardous         E                                   strength values
                                                         zone)                                                                 were given but,
                                                                                                                               as they exceed
                                                         Exceeding 1000 V/m rms           human           both    rotating     corresponding
                                                         electric field strength          occupancy                            rms electric
                                                         (danger zone)                    prohibited                           field values, only
                                                                                          (ceiling level)                      these are used in
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

                                                         up to 7 V/m rms electric         unlimited       both    rotating     practice, as the
                                                         field strength (safe zone)       (implicit                            limiting factor in
                                                                                          general                              permissible
                                                                                          population)                          exposure values.
                                                                                                                               Compare Fig.
                                                                                                                               21 and Fig. 22.
                                      10 MHz-300 MHz     7 V/m-20 V/m rms electric        working day                          E = ams electric
                                                         field strength (intermediate                                          field strength.
                                                         20 V/m-300 V/m rms electric      3200            both    rotating
                                                         field strength (hazardous        E2
                                                         zone)

                                                         Exceeding 300 V/m rms            human           both    rotating
                                                         electric field strength          occupancy
                                                         (danger zone)                    prohibited
                                                                                          (ceiling level)
    Sweden

    Workers           National        10-300 MHz         5 mW/cm2                         8 h             both    rotating
    Protection        occupational    0.3-300 GHz        1 mW/cm2                         8 h
    Authority         safety          0.3-300 GHz        1-25 mW/cm2                      60              both    rotating     P = power density
    (1976)            regulation                                                          P                                    mW/cm2.
                                      10 MHz-300 GHz     25 mW/cm2                        averaged        both    rotating     Ceiling level.
                                                                                          over
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

     USA

    American          Occupational    10 MHz-300 GHz     10 mW/cm2                        no limit (for   both    both         Under "moderate
    National          voluntary                                                           periods of                           environmental"
    Standards         consensus                                                           0.1 h or more)                       conditions, people
    Institute         standard                                                                                                 with circulatory
    (ANSI)            (recommendation)                                                                                         difficulties and
    (1966)                                                                                                                     certain other
                                                                                                                               ailments are
                                                         1 mWh/cm2                        during any      both    both         more vulnerable.
                                                                                          0.1-h period                         Techniques end
                                                                                                                               instrumentation
    ANSI (1974)       Occupational    10 MHz-300 GHz     10 mW/cm2 power density          no limit        cw      both         for measurements
                      voluntary                          200 V/m electric field strength                                       are given in
                      consensus                          0.5 A/m magnetic field                                                ANSI-C95.3-1973
                      standard                           strength                                                              publication.
                      (recommendation)                                                                                         Prevention of
                                                                                                                               associated hazards
                                                                                                                               -- see Institute
                                                                                                                               of Makers of
                                                                                                                               Explosives (1971).
                                                         10 mW/cm2 power density          0.1 h           pulsed  both         The US Department
                                                         1 mWh/cm2 energy density                                              of Labour adopted
                                                         40 000 V2/m2 mean squared                                             the ANSI 1968
                                                         electric field strength (E2)                                          standard in its
                                                         0.25 A2/m2 mean squared                                               proposed rules
                                                         magnetic field strength (A2)                                          (Fed. Register,
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

                                                                                                                               Vol. 38, No.
                                                                                                                               166, para 1910,
                                                                                                                               345, p. 23046,
                                                                                                                               1973) and finally
                                                                                                                               adopted 10 mW/cm2
                                                                                                                               as maximum safe
                                                                                                                               exposure limit
                                                                                                                               for occupational
                                                                                                                               exposure (Fed.
                                                                                                                               Register, Vol. 40.
                                                                                                                               No. 59, point 12,
                                                                                                                               p. 13138, 1975).
                                                                                                                               This standard is
                                                                                                                               a recommendation
                                                                                                                               and the Dept of
                                                                                                                               Labour is
                                                                                                                               preparing a new
                                                                                                                               standard.

    ANSI (1979)       Draft proposal  0.3-3 MHz          100 mW/cm2 power density         no limit,       both    both         Mean squared
                      for voluntary                      400 000 V2/m2-E2                 averaged over                        electric field
                      consensus                          2.5 A2/m2-H2                     any 0.1-h                            strength (E2)
                      standard                                                            period                               and mean squared
                      (recommendation)                                                                                         magnetic field
                                                                                                                               strength (H2)
                                                                                                                               are applicable to
                                                                                                                               near-field
                                                                                                                               exposures.
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

                                      3-30 MHz           900 mW/cm2 - power density       averaged over   both    both         f is the frequency
                                                         f2                               any 0.1-h                            in MHz.
                                                                                          period
                                                         4000  900  V2/m2 - E2
                                                             f2

                                                         0.025  900  A2/m2 - H2
                                                             f2

                                      30-300 MHz         1.0 mW/cm2 power density         averaged over   both    both
                                                         4000 V2/m2-E2                    any 0.1-h
                                                         0.025 A2/m2-H2                   period

                                      0.3-1.5 GHz        f     mW/cm2                     averaged over   both    both
                                                         300                              any 0.1-h
                                                                                          period

                                                         4000  f V2/m2-E2
                                                            300

                                                         0.025  f A2/m2-H2
                                                             300

                                      1.5-300 GHz        5 mW/cm2 power density           averaged over   both    both
                                                         20000 V2/m2-E2                   any 0.1-h
                                                         0.125 A2/m2-H2                   period
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

    American          Recommendation  10 MHz-100 GHz     Same as ANSI (1974)              same as ANSI    both    both         A ceiling level of
    Conference                                                                            (1974)                               25 mW/cm2 was
    of                                                                                                                         added to ANSI
    Governmental                                                                                                               (1974)
    Industrial                                                                                                                 recommendations.
    Hygienists                                                                                                                 Note: A legally
    (ACGIH)                                                                                                                    enforceable USA
    (1979)                                                                                                                     standard is an
                                                                                                                               equipment emission
                                                                                                                               standard for
                                                                                                                               microwave ovens
                                                                                                                               (US Code of
                                                                                                                               Federal
                                                                                                                               Regulations,
                                                                                                                               1970).

     USSR

    National          Occupational    60 kHz-3 MHz       50 V/m electric field strength   working day     both    both         Supersedes earlier
    Standards         national        3 MHz-30 MHz       20 V/m electric field strength                                        regulations
    Committee at      standard,       30 MHz-50 MHz      10 V/m electric field strength                                        and standards
    the Council       enforceable     50 MHz-300 MHz     5 V/m electric field strength                                         (section 9.2)
    of Ministers      by law          60 kHz-1.5 MHz     5 A/m magnetic field strength    working day     both    both         without essential
    of the USSR,                      30 KHz-50 Mhz      0.3 A/m magnetic field strength  working day     both    both         changes.
    1976 (USSR                        300 MHz-300 GHz    up to 0.1 W/m2 power density     working day     both    stationary
    Standard for                                         0.1 to 1.0 W/m2 power density    up to 2 h       both    stationary   During the
    Occupational                                                                          per day                              remainder of the
    Exposure,                                                                                                                  working day up to
    1976)                                                                                                                      0.1 W/m2.
                                                                                                                                               

    Table 18 (Cont'd)
                                                                                                                                               

    Country,
    agency, or        Type of                                                             Exposure        cw/     Antenna
    organization,     standard        Frequency          Exposure limit                   duration        pulsed  stationary/  Remarks
    date                                                                                                          rotating
                                                                                                                                               

                                      300 MHz-300 GHz    1.0 to 10 W/m2 power density     up to 20 min    both    stationary   During the
                                                                                          per day                              remainder of the
                                                                                                                               working day up to
                                                                                                                               0.1 W/m2.
                                                                                                                               protective goggles
                                                                                                                               are required.
                                      300 MHz-300 GHz    up to 1.0 W/m2 power density     during the      both    rotating
                                                                                          working day
                                                         1.0 to 10 W/m2 power density     up to 2 h       both    rotating     During the
                                                                                          per day                              remainder of the
                                                                                                                               working day up to
                                                                                                                               1.0 W/m2.
    Ministry of       Public health   see section 9.2
    Health            regulation
    Protection (USSR  enforceable
    Public Health     by law
    Standard,
    1978) (1978)
                                                                                                                                               
    

    10.  SAFETY PROCEDURES FOR OCCUPATIONALLY EXPOSED PERSONNEL

        Broadcasting, radio, radar, industrial heating, and medical
    equipment are essentially the same in all countries. Thus, the field
    strengths associated with different types of equipment will be similar
    and typical examples are shown in Fig. 22. In many instances, much
    higher field strengths may be encountered. Where personnel may be
    exposed to potentially high field strengths, they should receive
    appropriate training and be made aware of possible risks to health
    from the improper use of the equipment. This is especially important
    where the operation of equipment does not necessitate professional
    training or skills, e.g., plastic sealers. It is likely that service
    work or repairs will entail greater risk than operation since
    protective devices such as screens and interlocks would, in many
    cases, have to be rendered inoperable to carry out the servicing or
    repairs. Furthermore, service or repair personnel would generally be
    closer to the microwave/RF source.

        Reviews of safety procedures can be found in Mumford (1961), ANSI
    (1973), Minin (1974), Krylov & Jucenkova (1979), and National Health &
    Welfare, Canada (1979) (Safety Code 6).

    10.1  Procedures for Reducing Occupational Exposure

        The basic methods of controlling and limiting microwave/RF
    exposure, in order of desirability are: (a) engineering -- safe design
    and construction; (b) siting; (c) administrative; and (d) personnel
    protection.

        All unnecessary emissions should be minimized at the source,
    preferably by containment or otherwise effective screening. This
    approach is clearly impractical as far as the antenna system of
    deliberate emitters is concerned. In this case, siting can be very
    important in keeping both the number of people, who may be exposed,
    and the levels of exposure as low as possible. The same considerations
    apply where emission is unintentional but some leakage is unavoidable.

        Where people can be exposed to potentially hazardous levels,
    access to such areas should be controlled and restricted to persons
    who are trained and are aware of any risks. The use of special warning
    signs described in the Health and Welfare Canada Safety Code 6
    (National Health and Welfare, Canada, 1979) would be particularly
    useful. Time spent in the area should be kept as short as possible
    and, wherever practicable, microwave/RF power levels should be kept as
    low as readily achievable.

        The use of protective clothing is not generally recommended as it
    may initiate other hazards to the wearer, e.g., RF burns.

        For more detailed information, the reader is referred to the
    Health and Welfare Canada Safety Code 6 (National Health and Welfare,
    Canada, 1979).

    FIGURE 22

    11.  ASSESSMENT OF DATA ON BIOLOGICAL EFFECTS AND RECOMMENDED EXPOSURE
         LIMITS

        Major difficulties exist in assessing the potential health hazards
    to man of exposure to microwave and RF radiation, because of the
    highly complex relationship between the exposure conditions and the
    energy absorbed. The absorbed dose and rate of energy absorption
    depend critically on such variables as frequency, power density, field
    polarization, the size and shape of the exposed subject, and
    environmental factors. Many of the experiments contain insufficient
    information on the dosimetry, thus, difficulties arise in the exact
    interpretation of results.

        Experimental results indicate that most reported effects can be
    explained on the basis of microwave-induced, nonuniform heating.
    However, other investigations which have been carried out to evaluate
    the mechanisms involved, e.g., comparison of effects induced by
    microwaves with those produced by a water bath, indicate that
    nonthermal mechanisms may be involved. Further thorough studies of
    these nonthermal mechanisms are necessary, as their contribution to
    the understanding of microwave effects may be of great importance.

        Since most biological effects have been reported as phenomena,
    little information exists on quantitated dose-effect relationships.
    Studies on dose-effect threshold levels and their frequency dependence
    are badly needed in most areas. Because of the lack of such data,
    recommendations for exposure limits can only be made on the best
    available interpretations of the literature. Such interpretations also
    require an assessment of whether effects reported as phenomena truly
    present a hazard to health. Many effects are transient or easily
    reversible while others may cause permanent damage.

        From the summaries in sections 7 and 8, the following
    recommendations can be made:

    (a) Effects have been reported at power densities too low to produce
    biologically significant heating.

    (b) The occupationally-exposed population consists of healthy adults
    exposed under controlled conditions, who are aware of the occupational
    risk. The exposure of this population should be monitored.

        It is possible to indicate exposure limits from available
    information on biological effects, health effects, and risk
    evaluation. For workers, whole or partial body exposure to continuous
    or pulsed microwaves or Rf radiation having average power densities
    within the range 0.1-1 mW/cm2 includes a high enough safety factor
    to allow continuous exposure to microwaves/RF from any part of the
    frequency range, over the whole working day. Higher exposure may be

    permissible over part of the frequency range and for intermittent or
    occasional exposure. Special considerations may be indicated in the
    case of pregnant women.

    (c) The general population includes persons of different ages
    (infants, small children, young adults and senior citizens) and
    different states of health, including pregnant women. The possible
    greater susceptibility of the developing fetus to microwave/RF
    exposure may deserve special consideration. Exposure of the general
    population should be kept as low as possible and limits should
    generally be lower than those for occupational exposure.

        In view of the fact that data are still required to clarify
    interaction mechanisms and determine threshold levels for effects, it
    is recommended that microwave and RF exposure of
    occupationally-exposed workers and the general population should be
    kept as low as readily achievable.

        More precise exposure limits over the frequency range 100 kHz -
    300 GHz for both occupational and general population exposure to
    microwaves/RF will be recommended in follow-up documents.

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         Microwave Radiating Equipment. New York, Plenum Publ.,
        pp. 201-219.

    VARMA, M. M. & TRABOULAY, E. A. (1975) Biological effects of microwave
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    GLOSSARY

         Wherever possible, this glossary gives terms and definitions
    standardized by the International Electrotechnical Commission in the
    International Electrotechnical Vocabulary (IEV) or by the
    International Organization for Standardization (ISO). In such cases,
    the IEV number, or the number of the ISO standard in which the
    definition appears, is given in parentheses. The great majority of the
    terms and definitions are those of the IEV, and the help of Mr C. J.
    Stanford, General Secretary, International Electrotechnical
    Commission, in compiling the necessary information is gratefully
    acknowledged.

        An annex at the end of the glossary includes a number of
    additional terms that have not been standardized.

     absorption In radio wave propagation, attenuation of a radio wave
        due to its energy being dissipated, i.e., converted into another
        form such as heat (IEV 60-20-105).

     absorption cross-section; effective area Of an [antenna], oriented
        for maximum power absorption unless otherwise stated, an area
        determined by dividing the maximum power absorbed from a plane
        wave by the incident power flux density, the load being matched to
        the [antenna] (IEV 60-32-035).

     admittance The current flowing in a circuit divided by the terminal
        voltage; the reciprocal of the impedance (IEV 05-40-035).

     antenna That part of a radio system which is designed to radiate
        electromagnetic waves into free space [or to receive them]. This
        does not include the transmission lines or waveguide to the
        radiator (IEV 60-30-005).

     antenna directivity See  directivity

     antenna gain See  power gain of an antenna

     antenna, dipole See  dipole

     antenna, horn See  horn

     antenna, isotropic See  isotropic radiator

     antenna pattern See  radiation pattern

     antenna scanning See  scanning

     attenuation The progressive diminution in space of certain
        quantities characteristic of a propagation phenomenon
        (IEV 05-03-115).

     attenuation coefficient The real part of the propagation
        coefficient. Synonym:  attenuation constant (deprecated)
        (IEV 55-05-255).

     bel; decibel Transmission units giving the ratio of two powers. The
        number of bels is equal to the logarithm to the base ten of the
        power ratio. The decibel is equal to one-tenth of a bel
        (IEV 55-05-120).

     coaxial pair Two conductors, one being a wire or tube coaxially
        surrounded by the other which is in the form of a tube
        (IEV 55-30-45). A cable consisting principally of one or more
        coaxial pairs is termed a coaxial cable (IEV 55-30-50).

     conductance The reciprocal of resistance (IEV 05-20-170). Symbol:
         G. Unit: siemens (S).

     conductivity The scalar or matrix quantity whose product by the
        electric field strength is the conduction current density
        (IEV 121-02-1). It is the reciprocal of resistivity.

     continuous wave A wave whose successive oscillations are, under
        steady-state conditions, identical.

     cross section A measure of the probability of a specified
        interaction between an incident radiation and a target particle or
        system of particles. It is the reaction rate per target particle
        for a specified process divided by the flux density of the
        incident radiation (microscopic cross section) (IEV 26-05-605).

     current density A vector of which the integral over a given surface
        is equal to the current flowing through the surface. The mean
        density in a linear conductor is equal to the current divided by
        the cross-sectional area of the conductor (IEV 05-20-045).

     cycle The complete range of states or values through which a
        phenomenon or periodic function passes before repeating itself
        identically (IEV 05-02-050).

     decibel See  bel

     dielectric constant See  permittivity

     dielectric (material) A material in which all of the energy required
        to establish an electric field in the material is recoverable when
        the field or impressed voltage is removed. A perfect dielectric
        has zero conductivity and all absorption phenomena are absent. A
        complete vacuum is the only known perfect dielectric.

     dielectric saturation Response of a dielectric in the limit of high
        electric field strengths, leading to a decrease of the real part
        of the permittivity with increasing field strength.

     dipole A centre-fed open [antenna] excited in such a way that the
        standing wave of current is symmetrical about the mid point of the
        [antenna] (IEV 60-34-005).

     directivity That property of an [antenna] by virtue of which it
        radiates more strongly in some directions than in others
        (IEV 60-32-130).

     displacement See  electric flux density

     dissipation factor The reciprocal of the  Q-factor (IEV 55-05-285).
        See  Q factor.

     duty factor The ratio of (1) the sum of pulse durations to (2) a
        stated averaging time. For repetitive phenomena, the averaging
        time is the pulse repetition period (IEV 531-18-15).

     duty ratio The ratio, for a given time interval, of the on-load
        duration to the total time (IEV 151-4-13).

     effective area See  absorption cross-section

     effective radiated power in a given direction The power supplied to
        the [antenna] multiplied by the gain of the [antenna] in that
        direction relative to a half-wave dipole (IEV 60-32-095).

     electric charge; quantity of electricity Integral of electric
        current over time (ISO 31/V). Symbol:  Q. Unit: coulomb (C).

     electric field strength A vector the value of which equals the force
        exerted on a quantity of electricity divided by this quantity and
        the direction of which is that of the force (IEV 05-15-45).

     electric flux Across a surface element, the scalar product of the
        surface element and the electric flux density (ISO 31/V).

     electric flux density A vector quantity whose divergence equals the
        electric volume charge density.  Note: In vacuo, it is at all
        points equal to the product of the electric field strength and the
        electric constant (IEV 121-01-21). Symbol:  D. Obsolete synonym:
        displacement.

     electric susceptibility The scalar or matrix quantity whose product
        by the electric field strength is the electric polarization
        (IEV 121-02-09).

     electromagnetic energy The energy stored in an electromagnetic field
        (IEV 121-01-39).

     electromagnetic wave A wave characterized by variations of the
        electric and magnetic fields (IEV 121-01-38).

     electrostatic field That portion of the total electromagnetic field
        produced by a current-carrying conductor or charge distribution,
        the energy of which returns to the conductor when the current
        ceases or the charge distribution goes to zero.

     energy density See  radiant energy density

     far zone See  radiation zone

     ferromagnetic material A material in which the predominant magnetic
        phenomenon is ferromagnetism.  Note: The atoms or ions have
        magnetic moments which, over certain regions (domains), are
        aligned approximately in the same direction even in the absence of
        an externally applied magnetic field. When such a field is
        applied, the resultant moments of the domains tend to align so
        that the material exhibits considerable permeability. The degree
        of alignment within a domain decreases with increasing temperature
        (IEV 901-01-29).

     ferromagnetism A phenomenon by which the magnetic moments of
        neighbouring atoms are aligned approximately in the same direction
        due to mutual interaction (IEV 901-01-28).

     field 1.  In a qualitative sense, a region of space in which
        certain phenomena occur. 2.  In a quantitative sense, a scalar or
        vector quantity the knowledge of which allows the effects of the
        field to be evaluated (IEV 05-01-040).

     field strength In radio wave propagation, the magnitude of a
        component of specified polarization of the electric or magnetic
        field. The term normally refers to the root-mean-square value of
        the electric field (IEV 60-20-070).

     flux See  electric flux, magnetic flux

     flux density See  electric flux density, magnetic flux density

     Fraunhofer region Of a transmitting [antenna] system, the region
        which is sufficiently remote from the [antenna] system for the
        wavelets arriving from the various parts of the system to be
        considered to follow parallel paths (IEV 60-32-60).

     free space An ideal, perfectly homogeneous medium possessing a
        dielectric constant of unity and in which there is nothing to
        reflect, refract, or absorb energy. A perfect vacuum possesses
        these qualities.

     frequency The reciprocal of  period, q.v.

     Fresnel region Of a transmitting [antenna] system, the region near
        the [antenna] system where the wavelets arriving from the various
        parts of the system cannot be considered to follow parallel paths
        (IEV 60-32-065).

     gain The increase in power between two points 1 and 2 at which the
        power is respectively  P 1 and  P 2, expressed by the ratio
         P 2/ P 1 in transmission units (IEV 55-05-185).

     H field See table

     horn An elementary [antenna] consisting of a waveguide in which one
        or more transverse dimensions increase towards the open end
        (IEV 60-36-055).

     impedance The complex representation of potential difference divided
        by the complex representation of current (ISO 31/V).

     impedance characteristic Of a uniform transmission line, the
        impedance with which one end of the line must be terminated in
        order that the impedance presented at the other end shall have the
        same value as the terminating impedance.  Note: The term is
        occasionally applied to a symmetrical two-terminal-pair network to
        denote the common value assumed by the two image impedances and
        the two iterative impedances (IEV 55-20-155).

     impedance, wave (at a given frequency) The ratio of the complex
        number (vector) representing the transverse electric field at a
        point, to that representing the transverse magnetic field at that
        point. The sign is so chosen that the real part is positive
        (IEV 62-05-095).

     induction field That part of the field of an [antenna] which is
        associated with a pulsation of energy to and fro between the
        [antenna] and the medium.  Note: The induction field extends
        theoretically over the whole of space, but is negligible compared
        with the radiation field except in the neighbourhood of the
        [antenna] (IEV 60-32-045).

     induction zone; near zone The region surrounding a transmitting
        [antenna] in which there is a significant pulsation of energy to
        and fro between the [antenna] and the medium.  Note: The magnetic
        field strength (multiplied by the impedance of space) and the
        electric field strength are inequal and, at distances less than
        one tenth of a wavelength from an [antenna], vary inversely as the
        square or cube or the distance, if the [antenna] is small compared
        with this distance (IEV 60-32-055).

     insertion loss The loss due to the insertion of a transducer between
        two impedances ZE (generator) and ZR (load) is the expression
        in transmission units of the ratio  P 1/ P 2 where  P 1 is
        the apparent power received by the load ZR before the insertion
        of the said transducer, and  P 2 is the apparent power received
        by the load ZR after the insertion of the said transducer
        (IEV 55-05-160). Unit: decibel (dB).

     irradiation, partial body Exposure of only part of the body to
        incident electromagnetic energy.

     irradiation, whole body Exposure of the entire body to incident
        electromagnetic energy.

     isotropic Having the same properties in all directions.

     isotropic radiator An [antenna] which radiates uniformly in all
        directions. This is a hypothetical concept used as a standard in
        connection with the gain function (IEV 60-32-110).

     joule The work done when the point of application of 1 ... unit of
        force [newton] moves a distance of 1 metre in the direction of the
        force (Comit international des Poids et Mesures, 1946).

     magnetic field strength An axial vector quantity which, together
        with magnetic induction, specifies a magnetic field at any point
        in space. It can be detected by a small magnetised needle, freely
        suspended, which sets itself in the direction of the field. The
        free suspension of the magnetised needle assumes, however, that
        the medium is fluid or that a small gap is provided of such a
        shape and in such a direction that free movement is possible. As
        long as the induction is solenoidal, the magnetic field is
        irrotational outside the spaces in which the current density is
        not zero, so that it derives a potential (non-uniform) therefrom.

            On the other hand, in the interior of currents, its curl, in
        the rationalised system, is equal to the vector current density,
        including the displacement current.

            The direction of the field is represented at every point by
        the axis of a small elongated solenoid, its intensity and
        direction being such that it counterbalances all magnetic effects

        in its interior, whilst the field intensity is equal to the linear
        current density of the solenoid (IEV 05-25-020). Symbol:  H.
        Unit: ampere per metre (A/m).

     magnetic flux The area integral of the magnetic flux density
        (IEV 901-01-04). Symbol:  PHI. Unit: weber (Wb).

     magnetic flux density A solenoidal axial vector quantity which at
        any point defines the magnetic field at that point. Its value is
        such that the force exerted on an electric charge at that point
        moving at a given velocity is equal to the charge multiplied by
        the vector product of the velocity and the magnetic flux density
        (IEV 901-01-03). Symbol:  B. Unit: tesla (T).

     microwaves Electromagnetic waves of sufficiently short wavelength
        that practical use can be made of waveguide and associated cavity
        techniques in their transmission and reception (IEV 60-02-025).
        ( Note: for the purposes of the foregoing document the term is
        taken to signify waves having an approximate frequency range of
        0.3-300 GHz).

     near zone See  induction zone

     peak envelope power Of a radio transmitter, the average power
        supplied to the [antenna] transmission line or specified
        artificial load by a transmitter during one radio frequency cycle
        at the highest crest of the modulation envelope, taken under
        conditions of normal operation (IEV 60-42-260).

     peak pulse amplitude See  pulse amplitude

     peak pulse output power The maximum value of output power during a
        stated time interval, spikes excluded (IEV 531-41-17).

     period The minimum interval of the independent variable after which
        the same characteristics of a periodic phenomenon recur
        (IEV 05-02-40). Symbol:  T. Unit: second (s).

     permeability The scalar or matrix quantity whose product by the
        magnetic field strength is the magnetic flux density.  Note: For
        isotropic media, the permeability is a scalar; for anisotropic
        media, a matrix (IEV 121-01-37). Synonym: absolute permeability.
        If the permeability of a material or medium is divided by the
        permeability of cacuum (magnetic constant)m the result is termed
         relative permeability. Symbol:  . Unit: henry per metre (H/m).

     permittivity; dielectric constant A constant giving the influence of
        an isotropic medium on the forces of attraction or repulsion
        between electrified bodies (IEV 05-15-120). Symbol:  E. Unit:
        Farad per metre (F/m).

     permittivity, relative The ratio of the permittivity of a dielectric
        to that of a vacuum (IEV 05-15-140). Symbol:  Er.

     phase Of a periodic phenomenon, the fraction of a period through
        which the time has advanced relative to an arbitrary time origin.

     phase change coefficient The imaginary part of the propagation
        coefficient.  Note: This coefficient determines the change of
        phase of the voltages or currents (IEV 55-05-260). Deprecated
        synonyms: phase constant, wavelength constant. Symbol:  .
        Unit: radian per metre (rad/m).

     polarization A vector quantity representing the state of dielectric
        polarization of a medium, and defined at each point of the medium
        by the dipole moment of the volume element surrounding that point,
        divided by the volume of that element (IEV 05-15-115).

     polarization, plane of In a linearly polarized wave, the fixed plane
        parallel to the direction of polarization and the direction of
        propagation.  Note: In optics the plane of polarization is normal
        to the plane defined above (IEV 60-20-010).

     potential, electric For electrostatic fields, a scalar quantity, the
        gradient of which, with reversed sign, is equal to the electric
        field strength (ISO 31/V; also IEV 05-15-050).

     power 1. Mean power, work (or energy) divided by the time in which
        this work (or energy) was produced or absorbed. In periodic
        phenomena, the average power during a period is generally taken.
        2. Instantaneous power, the limit of the average power when the
        interval of time considered becomes infinitely small
        (IEV 05-04-025). Symbol:  P. Unit: watt (W).

     power flux density; field intensity In radio wave propagation, the
        power crossing unit area normal to the direction of wave
        propagation (IEV 60-20-075). Symbol:  W. Unit: watts per square
        metre (W/m2).

     power gain The ratio, usually expressed in decibels, of (1) the
        output power of an [amplifying device] operated under stated
        conditions to (2) the driving power (IEV 531-17-26). Symbol:  G.

     power gain of an [antenna] (in a given direction) The ratio, usually
        expressed in decibels, of the power that would have to be supplied
        to a reference [antenna] to the power supplied to the [antenna]
        being considered, so that they produce the same field strength at
        the same distance in the same direction; unless otherwise
        specified, the gain is for the direction of maximum radiation; in
        each case the reference [antenna] and its direction of radiation

        must be specified, for example: half-wave loss-free dipole (the
        specified direction being in the equatorial plane), an isotropic
        radiator in space (IEV 60-32-115). Symbol:  G. Unit: decibel
        (dB).

     Poynting vector A vector, the flux of which through any surface
        represents the instantaneous electromagnetic power transmitted
        through this surface (IEV 05-03-85). Synonym: power flux density.

     propagation constant A complex constant characterizing the
        attenuation and phase change per unit of length of the current or
        voltages which are propagated along a uniform line supposed to be
        infinitely long (IEV 05-03-150). Symbol:  alpha.

     pulse amplitude The peak value of a pulse (IEVV 55-35-100).

     pulse duration The interval of time between the first and last
        instant at which the instantaneous value of a pulse (or of its
        envelope if a carrier frequency pulse is concerned) reaches a
        specified fraction of the peak amplitude (IEV 55-35-105).

     pulse output power The ratio of (1) the average output power to (2)
        the pulse duty factor (IEV 531-41-14).

     pulse repetition rate The average number of pulses in unit time
        during a specified period (IEV 55-35-125).

      Q A measure of the efficiency of a reactive circuit (especially an
        oscillating circuit) or a component thereof. Its precise
        definition depends on the nature of the circuit; for an
        oscillating system without lumped  L or  C it is equal to 2pi
        times the average energy stored in the field divided by the energy
        dissipated during one half cycle. Synonyms:  Q factor, quality
        factor.

     radar The use or radio waves, reflected or automatically
        retransmitted,  to gain information concerning a distant object.
         The measurement of range is usually included (IEV 60-72-005).

     radar scan See  scanning

     radiant flux (surface) density Quotient of the radiant flux at an
        element of the surface containing the point, by the area of that
        element (IEV 45-05-155). Symbol:  E. When this quantity relates
        to radiation incident on a surface, it is termed  irradiance;
        when it relates to radiation emitted from a surface, it is termed
         radiant exitance Symbol:  M (deprecated synonym: radiant
        emittance) (IEV 45-05-160/170). Unit: watts per square metre
        (W/m2).

     radiation field That part of the field of an [antenna] which is
        associated with an outward flow of energy (IEV 60-32-040).

     radiation zone; far zone The region sufficiently remote from a
        transmitting [antenna] for the energy in the wave to be considered
        as outward flowing.  Note: In free space, the magnetic field
        strength (multiplied by the impedance of space) and the electric
        field strength are equal in this region and, beyond the Fresnel
        region, vary inversely with distance from the [antenna]. The inner
        boundary of the radiation zone can be taken as one wavelength from
        the [antenna] if the [antenna] is small compared with this
        distance (IEV 60-32-050).

     radiant intensity For a source in a given direction, the radiant
        power leaving the source, or an element of the source, in an
        element of solid angle containing the given direction, divided by
        that element of solid angle (ISO 31/VI). Symbol:  I. Unit: watt
        per steradian (W/sr). With reference to antennas, this quantity is
        also called  radiated power per unit solid angle in a given
         direction (IEV 60-32-090).

     radiation pattern; radiation diagram; directivity pattern A diagram
        relating power flux density (or field strength) to direction
        relative to the [antenna] at a constant large distance from the
        [antenna].  Note: Such diagrams usually refer to planes or the
        surface of a cone containing the [antenna] and are usually
        normalized to the maximum value of the power flux density or field
        strength (IEV 60-32-135).

     radio frequency Any frequency at which electromagnetic radiation is
        useful for telecommunication (IEV 55-05-060). (See Annex).

     reactance Imaginary part of impedance (ISO 31/V). Symbol:  X. 
        Unit: ohm (OMEGA).

     reflected wave A wave, produced by an incident wave, which returns
        in the opposite direction to the incident wave after reflection at
        the point of transition (IEV 25-50-065).

     reflection coefficient; return current coefficient The complex ratio
        of reflected signal current to incident signal current at the
        termination (IEV 55-20-180). Symbol:  G.

     refractive index The ratio of the velocity of electromagnetic
        radiation  in vacuo to the phase velocity of electromagnetic
        radiation of a specified frequency in a medium (ISO 31/VI).
        Symbol:  eta.

     scanning Of a radar [antenna], systematic variation of the beam
        direction for search or angle tracking (IEV 60-72-095). The term
        is also applied to periodic motion of a radiocommunication
        antenna.

     scattering The process by which the propagation of electromagnetic
        waves is modified by one or more discontinuities in the medium
        which have lengths of the order of the wave length (IEV
        60-20-120); a process in which a change in direction or energy of
        an incident particle or incident radiation is caused by a
        collision with a particle or a system of particles (ISO 921). The
        extent to which the intensity of radiation is decreased in this
        manner is measured in terms of the  attenuation coefficient
         (scattering).

     scattering cross section The cross section for the scattering
        process (IEV 26-05-650). See  cross section; scattering.

     shield A mechanical barrier or enclosure provided for protection
        (IEV 151-01-18). The term is modified in accordance with the type
        of protection afforded; e.g., a magnetic shield is a shield
        designed to afford protection against magnetic fields.

     standing wave A state of vibration in which the oscillatory
        phenomena at all points are governed by the same time function,
        with the exception of a numerical factor, varying from one point
        to another (IEV 05-03-065).

     standing-wave ratio The ratio of the maximum to the minimum
        amplitude of the current, voltage or field, measured respectively
        at an adjacent node and antinode in a line or waveguide carrying a
        standing wave (IEV 60-32-235). Symbol:  (S).

     thermograph A term applied to a variety of instruments for measuring
        and recording temperature, especially (1) the heat radiated by the
        human body and (2) atmospheric temperature. The record produced by
        such an instrument is termed a  thermogram and the technique is
        termed  thermography. Note: None of these terms should be used in
        the context of thermal analysis, where they are deprecated.

     time constant On an exponentially varying quantity, time after which
        the quantity would reach its limit if it maintained its initial
        rate of variation. If a quantity is a function of time given by
         F(t) =  A +  Be -t/tau then tau is the time constant
        (ISO 31/II).

     transmission factor Ratio of the transmitted radiant ... flux to the
        incident flux (IEV 45-20-085).

     transmission loss Over a given transmission path and for a given
        frequency, the amount, expressed in decibels, by which the
        available power at the input to a receiver is less than that
        available from the output stage of a transmitter (IEV 60-20-100).

     wave A modification of the physical state of a medium which is
        propagated as a result of a local disturbance (IEV 05-03-005).

     wave, diffracted A wave caused by the scattering of an incident wave
        upon an obstacle (IEV 101-05-15).

     waveguide A system for the transmission of electromagnetic energy by
        a wave not of TEM type. It may, for example, consist of a metal
        tube, a dielectric rod or tube, or a single wire (IEV 62-10-005).

     wave incident A travelling wave before it reaches a transition point
        (IEV 25-50-055).

     wavelength The distance between two successive points of a periodic
        wave in the direction of propagation, in which the oscillation has
        the same phase (IEV 05-03-030). Symbol:  lambda. Unit: metre (m).

     wave, plane A wave such that the corresponding physical quantities
        are uniform in any plane perpendicular to a fixed direction
        (IEV 05-03-010).

     wave, transmitted A wave (or waves) produced by an incident wave
        which continue(s) beyond the transition point (IEV 25-50-060).

     wave, transverse A wave characterised by a vector at right angles to
        the direction of propagation (IEV 05-03-070).

    ANNEX

         The terms and explanations included in this annex are for the
    purposes of this publication only, and are not necessarily valid for
    any other purpose.

     athermal effect An effect in a living organism that occurs
        predominantly as a result of some phenomenon other than a local or
        whole body rise in temperature.

     depth of penetration For a plane-wave electromagnetic field incident
        on the boundary of a lossy medium, the depth of penetration of the
        wave is taken to be that depth at which the field strength of the
        wave has been reduced to 1/ e or approximately 37% of its
        original value.

     exposure, high level At the Warsaw symposium it was agreed that, in
        the microwave range, "high-level exposure"covers exposure to power
        flux densities exceeding 10 mW/cm2. There is no agreement as to
        the meaning of the term when applied to radiation in the RF range.

     exposure, intermittent This term refers to alternating periods of
        exposure and absence of exposure varying from a few seconds to
        several hours. If exposure lasting a few minutes to a few hours
        alternates with periods of absence of exposure lasting 18-24 hours
        (exposure repeated on successive days), "repeated exposure" might
        be a more appropriate term.

     exposure, long-term This term indicates exposure during a major part
        of the lifetime of the animal involved; it may, therefore, vary
        from a few weeks to many years in duration.

     exposure, low-level At the Warsaw symposium it was agreed that, in
        the microwave range, "low-level exposure" covers exposure to power
        flux densities up to 1 mW/cm2. There is no agreement on the
        meaning of the term when applied to radiation in the RF range.

     exposure, medium-level At the Warsaw symposium it was agreed that,
        in the microwave range, "medium-level exposure" covers exposure to
        power flux densities of 1-10 mW/cm2. There is no agreement on
        the meaning of the term when applied to radiation in the RF range.

     exposure, repeated This term refers to exposures lasting from a few
        minutes to a few hours repeated on successive days.

     exposure, short-term This term covers exposures lasting from a few
        hours to 24 hours, or exposures for a few hours per day repeated
        for a few days per week.

     exposure, single This term usually refers to an uninterrupted
        short-term exposure.

     non-thermal effect See  athermal effect.

     radiofrequency In the present document, this term is used to
        designate frequencies ranging from 100 kHz to 300 MHz.

     thermal effect An effect resulting predominantly from a local or
        whole body temperature rise in the living organism.
    


    See Also:
       Toxicological Abbreviations